I think this is a really first rate video. You covered a confusing topic with clear, concise, and thorough explanations.
@14112ido7 жыл бұрын
James Kelson no wonder though, he is a teacher. Explaining things is literally what he does for a living :).
@hotchihuahua15464 жыл бұрын
@@14112ido I have looked at many explanations, even one based on sound that he mentions ! When we are doing our own tuning the bottom line is getting the right information so we don’t chase our tails ! 😁
@StonyRC7 жыл бұрын
YOU'VE DONE IT AGAIN! I've watched a number of other videos that try to explain Tiller and you are the only one that really explains it PROPERLY. Many thanks NUSensei, your words of wisdom are a constant help to an aspiring archer like me ;-)
@rapmamori41362 жыл бұрын
New to archery and still waiting for my first bow. Its so nice to watch and learn from Nusensei, he sounds like a very eloquent professor.
@Uthael_Kileanea Жыл бұрын
Just watching some basic bow building video. Paused and went to look "What's a tiller?". My first time hearing about it. Thanks a bunch!
@carls262210 ай бұрын
Great instruction, best explanation I've heard so far.
@MrWolfverin3 жыл бұрын
Thank you for clearing my doubts about bow tiller. Excellence explanation why tiller happens and why and when we should do the adjustment. Simply Awesome ! Thank you .
@PedroCL8 жыл бұрын
Good video - a practical example of how to set up, tune or define your tiller would be a nice follow up.
@Kuhtlass3 жыл бұрын
Deserves more views. You broke it down much easier than some of these other vids on here.
now, i really understand what bow tiller n why important....thanks NUsensi you explain well
@blacktopknowledge3 жыл бұрын
Very informative and helpful, I’m building my first asymmetrical flatbow and wasn’t quite understanding positive tiller but after your explanation I believe I have a fair understanding now thank you
@justice626757 жыл бұрын
Big fan. Can watch your videos over and over. Thanks for all the clear technical instructions.
@Pavic1246 жыл бұрын
I really like how you can explain these concepts so easily. Thanks for the information.
@rogberube64223 ай бұрын
Excellent tutorial. Thanks for sharing.
@This1sEngland3 жыл бұрын
Thanks for this vid. I'm just getting into Olympic recurve archer after 2 years of Trad bow. I am still three under, but will be trying split finger, so I will need to change my neutral tiller and now I know how too. Cheers NUSensei
@61zulu77 Жыл бұрын
Best video on the tiller concept!
@airbutz5 жыл бұрын
Excellent explanation - thanks very much for taking the time to get this info to us and making me a little bit smarter.. Greets from Switzerland
@tumbleweed-life4 жыл бұрын
You just turned the lights on for me! I just got a new bow and going to set it up for Barebow and string walking so this will help with set up. Thanks
@This1sEngland3 жыл бұрын
Then you need a negative tiller of about 1/8", so your ring finger does not get squashed as you string walk. This will also stop you fighting the bow and you will notice the bow after firing punches forwards instead of upwards and forwards. Got that advice from Jake Kaminski who has now entered the journey into Barebow from Olympic recurve archery.
@handpan-relaxingmeditation33164 жыл бұрын
very good explained. thank you.
@frankiebob73457 жыл бұрын
Best video on tiller out there! Thank you for sharing your knowledge. Only comment measuring a one piece bow from the point it starts to curve is a hard location to find in any repeatable way. Most measure where the material of the riser break out ends because its easier to locate. Where the riser material is razor thin for some distance I find where it is a specific minimum thickness like 2 mm and just use that spot to measure.
@FreedomInMindtv5 жыл бұрын
Excellent video! Very helpful, thanks mate 👍🏻
@thephoenicianarcher52672 жыл бұрын
Im very happy that i found this video thank you coach this is very rich information.
@NicholeRojas-r8i6 жыл бұрын
Thank you for making these videos! They are so informative! I've understood many things thank you very much!
@DarthGold8 жыл бұрын
Excellent, now i understand tiller finally
@timkopacsi7517 Жыл бұрын
Love your channel thanks for all the info.
@dperk17574 жыл бұрын
Excellent video 👍
@riccoratzo6 жыл бұрын
Thank you for explaining everything in a easy way, your Videos are very helpfull!
@bisouillzbisouillz45178 жыл бұрын
Thanks from France! Excellent video
@Bizahaaaa2 жыл бұрын
Great explanation
@Jim-lq1vq5 жыл бұрын
Excellent discussion on tiller adjustment. I am trying to change a bow to bare bow style shot with string walking and this was just what I needed as I was having excessive limb noise with a positive tiller as I had used the bow for olympic style.
@matthias75223 жыл бұрын
Perfect explenation, thank you!
@skeezixcodejedi8 жыл бұрын
Outstanding video; thanks!
@PennsylvaniaSasquatch7 жыл бұрын
Thanks for clearing up a topic that can be quite confusing : )
@raulespindola7636 жыл бұрын
As always, great video... Thank you!
@peterandtyson55028 жыл бұрын
Loved your syndicate vid
@dkveracity65able2 жыл бұрын
Out of curiosity, say on a take down bow with a even neutral tiller. Do you need to place a thin washer or wedge between your riser and limb, or do you leave your upper limb bolt loose and top limb "flapping for string tension?" This question is for cheaper takedowns that have no lock bolts . Thanks.
@woodman01313 жыл бұрын
Very helpful. Thanks!
@PaulXerxen Жыл бұрын
Standard method in Olympic style shooting is definitely splits finger, but for barebow shooting its 3 under as you can't string walk any other way.
@ianbelgarde97797 жыл бұрын
1:34 Did you mean grow? You cant shrink from 1/8th to 1/4. thats growth. Did you mean to say 'shrink to 1/16th'?
@ThePiraguista7 жыл бұрын
I'm attempting to make my own recurve bow, i've never shooted one, but i love the crafting process, and I also find archery very interesting so i'll give it a try The point is that I dont know how it will come out, but I undesrtand that I should shoot in a way or another depending on the tillering I get, right? Since I'll be doing my own limbs too, out of fiberglass, they may not have the same draw weight so I'll put the stiffer dow
@Redsnake78198 жыл бұрын
Excellent video
@peterbartley97776 жыл бұрын
Good explanation.
@gaga2b6 жыл бұрын
My Sensei I have a question about when carrying a bow strung up and ready for use in the woods for target and or bow hunting with a compound , recurve and long bow. How do you carry a bow when going into a wooded area along with quiver and target bag? Is it how Legolas does it?
@dankolord Жыл бұрын
How do those tiller bolts work? Why do they change the tiller?
@sprk115 жыл бұрын
thank you I'm looking at the tiller now as a way to make my bow shoot better. And I have been moving my knock point around to find where it feels best and as you say this is one way to balance out your draw weight I'll leave it with that. Now all that said I find that each time I set up new arrows I have to change or feel I need to change the knock point. Does this sound correct to you or am I perhaps a bit mental.
@clericneokun8 жыл бұрын
It would be nice if I manage to find the actual mathematical formula for computing the proper positive tiller in relation to the distance between the arrow rest and the center of the bow.
@ZolcsiBB8 жыл бұрын
mark2500 and how do you calculate with the uneven tension between your draw fingers? Also your bow hand pressure point? And the effect of your stabiliser system? It is not something you can calculate. These kind of calculations are deep into FEM territory. You can find the answer quicker if you just go out and tune the bow. :)
@clericneokun8 жыл бұрын
ZolcsiBB If you're just going to tell me to wing it until it "feels right" then you've just negated the whole point of this video. Also, I don't consider bow tuning as a crutch to deal with my own imperfections. The bow is its own entity and I develop my technique to utilize that entity as efficiently as possible. Same goes with whatever peripherals I attach to it. So far, I'm stuck with only the guidelines and the only way to make any meaningful adjustments is through observation of output and I'm currently in the process of acquiring my own high performance camera to capture the bow at work in slow motion. This should help me with not only tiller but also trouble shooting anything from arrow flight and my own form problems. Sorry but I'm just the kind of guy that enjoys the mechanics more than the actual shooting.
@ZolcsiBB8 жыл бұрын
mark2500 I am an engineer myself, so I think I understand where you come from. I also like to think a lot about how things work. But archery usually rewards more (quality-) practice and less over-thinking. There is no mathematical formula for archery. The high speed camera could be a good practical idea, but you will need several thousand FPS for your needs. If you can afford access to a studio with equipment like that, you are lucky indeed! But I still think that you will not find the holy grail there. :)
@clericneokun8 жыл бұрын
It's alright. Not like I'm looking for some shortcut to success or anything. Even though it's already been a year since I started, nothing else still feels more rewarding to me than discovering new ideas and techniques. The medals are just there to stuff inside the cabinet. I'm honestly not into that tournament stuff unless my friends bug me to join them. Speaking of the camera, me and my friend once used a Galaxy S7 that he borrowed from the company he worked for (they used it for testing prototype apps or something). The hardware was surprisingly good enough to capture a person's finger release as well as arrow flight in great detail. I'm thinking of buying one and a tripod and simply go to town on that thing. That should be pretty fun. ^_^
@ZolcsiBB8 жыл бұрын
mark2500 If I can suggest one more thing: video delay app for Android. You set it up with the selfie camera and set the delay to 8 seconds. After you shoot, you can immediately see your technique in a replay. Helps a lot!
@zulamer24355 жыл бұрын
Hi Nusensei, some manufacturer suggestion for limb tiller is 0-5mm, does that mean the limb can be used even in neutral tiller?
@dylanfrancisbravener85134 жыл бұрын
Thx Nu! 😘🏹🎯
@frankwilliams54757 жыл бұрын
Excellent. Very well done. Great information. Thank you.
@michaelenelmar8 жыл бұрын
Really nice video! Finally I'm getting closer to what I'm searching for a while: I'm into instinctive shooting but still like the high tech aspect of archery. So I finally decided to go for an olympic recurve, but bareboned. I'm shooting three under, so what kind of tiller would you recommend? I guess I can estimate a neutral or slightly negative tiller by imagining the center of force in my hand, right? Thanks and enjoy.
@douglasrice85485 жыл бұрын
Do to your great videos I'm looking at the Mandarin duck windrunner and I've decided I want to be a stringwalker. Will this bow work OK?
@NUSensei5 жыл бұрын
Sure, it works as well as any bow.
@lupusverdi2 жыл бұрын
My biggest problem is I can never set it the way I want it. If I want a certain tiller, which screw do I turn? How far do I turn it? I always overshoot and get ridiculous measurements. What I don‘t understand is: how is for example 1/8 of a turn affecting the angle? I don‘t have any reference points to easily see what I‘m doing. Most of the time I spent hours correcting, overshooting again and somehow eventually getting the correct measurement. What am I doing wrong? It‘s just so finicky
@Guy-ky9mc2 жыл бұрын
Uh oh.. my upper is less distance than the lower. Lower is showing 7.75" and the upper is 7.25". So mine is negative? I think my upper limb is for 55lb and my lower is for 50lb. I've noticed my arrows nosediving at launch for the first 10 yards. I kept trying different nocking points to get arrow straight but I suspect it's all because the upper limb is stronger. I shoot 3 under so maybe I'll string walk to see if it smooths out the nosedive issue. Or flip the limbs so the 55lb limb is on bottom just to test.
@luverneanimatics87695 жыл бұрын
I have a neutral tiller with a wooden riser is it normal for a wooden riser to have neutral tiller?
@HansPeter-qg2vc7 жыл бұрын
What about compound bows? On my bow, the limbs are exactly equally far away from the string. But the D loop is 125 mm closer to the top cam than to the bottom cam. The limbs are exactly equally long and look identical. The cams look identical, too. Why is this?
@kmarchery8 жыл бұрын
hi nu sence . that first bow . the one piece . is that a chek mate ?? I thought the logo sticker looked like the chek mate one but it's at an angle and of course you are. moving it
@peterelkelton49616 жыл бұрын
Is tiller necessary if the arrow is centered?
@social3ngin33rin8 жыл бұрын
What do you think about "Loctite for nuts and bolts" being used on the tiller? :) You mentioned that some people have ones that loosen.
@mackemforever8 жыл бұрын
Loctite will not stop you from undoing a bolt, it will however stop a bolt from coming loose due to the vibrations from shooting. Of course undoing a bolt that has been loctited in place is harder work than it would be without the loctite but it is still easily possible.
@social3ngin33rin8 жыл бұрын
yes I know :) It's great for use in guns and gear I wasn't sure how it would be in an archery setting for a bow >_>
@bmackoutdoors42826 жыл бұрын
I bought new take down recurve how can I get positive tiller adjust on bottom limb but not too sorry newby
@wanr57018 жыл бұрын
do you think when the limbs come in pair, the bottom one is already slightly heavier than the top when in neutral tiller?
@NUSensei8 жыл бұрын
No, the limbs would be manufactured to be identical. Tiller is a function of the riser (for takedown bows), and from what I know, most bows either have neutral tiller or positive tiller when bought - though just ambiguous enough for either style to be shot.
@wanr57018 жыл бұрын
NUSensei thanks. because i always curious why limbs are always marked top and bottom. must be some reason they do that, otherwise we can alternate the limbs with no differences in shooting.
@annguyen38928 жыл бұрын
I was wondering the same thing, why do they mark limbs top and bottom if they are supposed to be identical.
@ZolcsiBB8 жыл бұрын
Depends on the manufacturer. As I know, some make them identical, some "include tiller". You can check yours by setting both bolts identical, then measure. However, it doesn't matter. What matters is how you tune the whole system.
@suepalsbo81498 жыл бұрын
The arc of the upper limb is different from the arc on the lower limb. If you put them side by side on a table and run your hand up to the tips, you can feel the difference, even in low-poundage Samick limbs. The lower limb has a greater arc than the upper. The difference feels more pronounced with heavier limbs, and with some limbs you can see it very easily. The different limb arc is another way (in addition to tiller) to compensate for holding the grip below the pivot point, and the tips of the limbs moving different distances. You can probably explain this better than I just did.
@Diggs50128 жыл бұрын
I swapped my limbs on my Sage, top limb w/ bottom, 35lb limbs and noticed it shot no differently. I was adjusting for a slight twist in the light draw bow. I swapped them back however. I will check it out again. I bought a PSE 50lb recurve and the previous owner had limbs backwards lol oops for him. Peace great work on ur videos bro
@magehunter33668 жыл бұрын
If top limb is longer than bottom, your previous owner deliberately reversed them to create a negative tiller to shoot string walk
@literaryartist16 жыл бұрын
So on compounds tiller is "non-existant"? Meaning the "cam timing" is the equivalent to "tiller" on recurves and longbows?
@PurpleDracos6 жыл бұрын
Depending on the compound tiller is pretty hard to measure especially with beyond parallel limbs. From experience tiller on a compound does a slightly different thing to tiller on a recurve. Cam timing is as you say a pretty good analogy to recurve tiller getting the limbs to unfurl at the same speed and you must get good cam timing for the bow to function decently. Where the tiller comes in is that it can affect the vertical nock travel which affects how straight the arrow leaves the bow. Some compounds get a good level nock travel by having the grip below the centre of the bow and have the arrow pass through the centre, other compounds like recurves have the throat of the grip at the centre and arrow above centre so a small tiller adjustment may be required to get better nock travel if the limbs have not been manufactured to take account of the uneven pull. Tiller adjustments can also help with aiming as well on a compound as it can affect how steady the bow naturally holds, if you have a slight upward or downward movement of the sight while at full draw turning one limb bolt slightly one way or the may steady this, of course to maintaining draw weight you should then try to move half the distance turned back and then move the other bolt this half distance in the opposite direction the the original bolt and see if the steadiness is maintained.
@RotorMedic77 жыл бұрын
GREAT EXPLANATION! Thank you.
@ashravenpb8 жыл бұрын
So, when I draw my bow, I use one finger above and two under. However when I'm at full draw I release the bottom finger, so Im holding with 2 fingers. Should I correct this when I move to recurve and will it cause problems?
@NUSensei8 жыл бұрын
This is generally regarded as a form fault. I've seen some archers remove a finger when at full draw, and the consequential release is terrible. Too stressful, little control. A two-finger release can be done, but there isn't much reason to do so.
@ashravenpb8 жыл бұрын
Thanks, I'll work on correcting it
@llViperStrikerll8 жыл бұрын
So you did decide to make a video on this after all.
@thekenyancush56506 жыл бұрын
Thank you❤️❤️
@Marcus_from_OZ5 жыл бұрын
Thank you.
@wayne2wax6 жыл бұрын
please help me . . . . . . . . . "assume" One uses 2-under, 1-above DRAW with a Finger-Tab. Assume One always re-adjusts String's Nok-set to same position on string w.r.t. Rest (for Nocking Arrow to string, same way). Assume default TILLER was set to Bottom-limb=7.0625" & Top-limb=7.375". . . . . . . . . . Now please help with what happens NEXT ..... if TILLER is CHANGED to Bottom-limb=6.875" & Top-limb=8.000" , will the Arrow arrive on the target higher up the face, or lower down on the face???? Also, if TILLER is CHANGED to Bottom-limb=7.5" & Top-limb=7.125" , will the Arrow arrive on the target opposite way to first [changing to EXTREME positive tiller] example {using the slight/minor Negative tiller}???? What does practical science demonstrate happens to arrow trajectory ???? Please help me ? ?
@Hawkquill6 жыл бұрын
Thanks very clear
@YTMegiddo7 жыл бұрын
This explains a very odd looking long bow my great grand father had. There was an obvious difference. I had no idea what the deal was. Edit: It might not have been a long bow, but as a kid... it was pretty long! :)
@stevenarango29297 жыл бұрын
great video ty,,,,,,,
@Mekratrig6 жыл бұрын
I don’t get it (no surprise, am not an archer). Why not design the bow with the nock point and ‘shelf’ where the arrow rests at the center, and the grip below. Seems like that would simplify things a great deal.
@NUSensei6 жыл бұрын
An asymmetric grip would make it less practical for the human anatomy. We get a better grip and draw when things are centred. If we lowered the grip, which isn't easily possible due to the shape of the bow. It will also affect how we have to hold it (i.e. it is much lower than normal).
@TerekkiTerekki4 жыл бұрын
TY
@JFizoust5 жыл бұрын
Hi everyone. My names Feezy, I'm an archerer, and I'm addicted to math.
@lhasakivan6 жыл бұрын
Thank You Thank You Thank You... Please teach and share the KZbinr "Shoreshot Archery" How to verbally present clear and clean information without personal fluffy opinions. He tries to be cute in digression and maudlin verbiage that only confuses listeners in search of didactic information.
@MitsubishiPajeroAus8 жыл бұрын
Nu tiller the hun
@datgreedymouse68606 жыл бұрын
Hevier? You mean thicker?
@PurpleDracos6 жыл бұрын
Heavier can mean thicker which might be the case for a bow with neutral tiller to get the same effect as a positive tiller. In this case though it means it takes more force to deflect the limb by a certain amount. The tiller adjustment changes the geometry of the limbs slightly meaning the tips unfurl differently and the force required to move them is changed.
@lhasakivan6 жыл бұрын
YOU DESCRIBED THE REASONS FOR A CERTAIN TUNINGS IN TILLERING BUT YOU FAIL, FAIL, FAILED TO SIMPLY STATE "HOW TO GET AN EVEN TILLER BY SCREWING THE BOTTOM LIMB BOLT "IN" OR"OUT" TO GET AN EVEN TILLER.... SO "HOW" DO YOU "ADJUST" THE BOTTOM LIMB (WHICH IS 1/2" CLOSER TO THE RISER) DO I SCREW THE LIMB BOLT IN OR OUT TO GET AN EVEN TILLER? SO IF MY BRACE HEIGHT IS 9.25" AND MY TOP TILLER OR LIMB MEASURES 8"; AND THE BOTTOM MEASURE IS 7.5" CURRENTLY ... DO I SCREW THE BOLT "IN" OR OUT TO GET THE BOTTOM LIMB TO BE 8" LIKE THE TOP LIMB???
@lubossoltes3218 жыл бұрын
very good video, just one correction, you cannot string walk with split-finger (saying three under or string walk does not make sense in this case :-)). you can gap with three under (I shoot that way) or split-finger.
@wernersalzl16504 жыл бұрын
You showed 89 degrees. of angle.
@TheLang0lier4 ай бұрын
Alles klar jetzt.
@harrychen5747 жыл бұрын
I will have to respectfully disagree with you, Nu Sensei. This will be pretty long winded, but please bear with me. This will be explained based on the notion that the manufacturers have somehow decided to make the upper and lower limbs the same. It's probably an economic decision. You mentioned that in the case of a split finger, a positive tiller is called for because by drawing above the center, the top limb is closer to you than the bottom limb. That is in fact a false sense. In this case you have taken the perspective of your being a datum of measurement from your face. In the event that you were an alien with your head below your shoulders and your draw to anchor to the top of your head, the bottom limb would be closer to you. This evaluation of "closeness" is irrelevant from the standpoint of the bow itself, and therefore fails to explain why a positive tiller is required. The real reason for a positive tiller is as what you have broadly defined, a sort of "cam timing" analogous to compound. The real question in this case is why it has to be positive. Based on the compound analogy, I will now further expand on their similarities. When dealing with a two cam system, it is imperative that they achieve some sort of synchronous action. This synchronous action also demands that they bow start off the same i.e. at the same "gearing". Imagine two cars starting from zero to 60MPH, with one car on the first gear, and the other on a second gear. In most normal cases, the car that starts off on the first gear will achieve 60MPH in the shorter time, within a shorter distance. A two cam compound system is in fact an infinite series of gear deployment, evident from the varying lever ratio between the load (perpendicular string to axel distance) and the effort (perpendicular cable to axel distance), through the shot sequence. It can be adequately described as beginning from a low gear (higher cable distance than string distance from the axel) and gradually building up to a high gear (higher string distance than cable distance from the axel) in the case of a low let off cam, such as the Hoyt Spiral cams, giving it the superior speed performances when compared to other classes of higher let off cams. When you look at a recurve at full draw, it mimics this low to high gear characteristic, by having the outer tips retract to their rest positions first, leaving the inner portions either stationary, or outright in reverse motion near the limb butt. As the shot progresses, this retraction begins to build in terms of a larger proportion of the outer parts of the limb having a forward motion, with the tension of the string mostly remaining constant, similar to the situation of a high gear motion. It is this incremental increase in "gear" that provides the recurve bow with the high speeds achieved. At this point most of you would have lost me but let me continue in the next paragraph. When you turn the lower limb bolts into the riser to increase the positive tiller, you are not making the lower limb experience a stronger loading than the upper limb. It is in fact the opposite. The upper limb becomes more loaded. Since both limbs share the same string, they should be at the same tension, but that is only true when you talk about the string. If at this point you have completely lost me, think about fishing. When you leverage harder on the lower "rod", the fish on the upper limb fighting with the string is now yielding more to the increase in the effort used on the lower "rod". Now bring this all the way to the extreme and increase the tension until the string contacts the lower limb. See the picture? What positive tiller does, is to establish a common starting point in terms of gear ratio AT FULL DRAW. The reason it has to be positive, has everything to do with the main pressure point of the hand on the bow, being NOT AT THE GRIP THROAT, but at the lower portion, where the radius of the bow arm directs its force forward through the base of the thumb. This point is below the center of the riser, with the nocking point being above the center of the string, forming a downward tilting bow expanding vector. The lower limb in fact experiences a higher transition than the upper limb from brace to full draw, if one were to trace the paths taken by the two limb and compare them, because the bow arm is pushing the lower part of the bow. Limb loading during the draw is heavily affected by receding dead zones on the limbs, dead zones being the portion of the limbs still in contact with the string, in theory rendering that portion "unused". Having the lower limb set with a larger dead zone than the upper limb (in the case of positive tiller settings) ensures that by the time full draw is achieved, both upper and lower limbs are at equal footing. One interesting extrapolation of this theory predicts the increase in positive tiller settings for folks with larger hands, all else being equal. And that's the reason why you have positive tiller settings. Thank you all for kind your attention. Please don't attack me, I'm just a bored fat asian dude.
@Siberius-7 жыл бұрын
With the first longer paragraph.. wasn't he talking about the draw in relation to the centre of the bow where the grip is?.. I don't recall him mentioning the human..
@harrychen5747 жыл бұрын
The human is very much a part of the shooting system for recurve. More so than a compound. To exclude the human body from the analysis, is to commit a grave mistake.
@Siberius-7 жыл бұрын
That's not what I said.. I know humans shoot bows.. I'm saying that where the head/face is.. doesnt matter and he never said it did matter.. he never even talked about that. It's about where the centre of the bow is, with what type of draw you use. Then placing the nock accordingly to compensate if you use the 3 under draw. But that's not needed if you use the split finger draw. Not because of the face.. the face is irrelevant.
@harrychen5747 жыл бұрын
3:12.
@harrychen5747 жыл бұрын
I know he didn't talk about that. And that's the reason why I highlighted it. His assumption that the upper limb is closer to him, is in fact an illusion, and the explanation of how the illusion came to be, is the fact that he is using his face as a datum of measurement.