[doikor]

This happens in swimming because of the tolerance of making an olympic spec pool. A good swimmer goes a bit over 2mm every 0.001s. The pools have 3cm tolerance meaning the lanes are not the exact same length (it would be crazy expensive to make pools to smaller tolerances)

So to solve this they just don't measure beyond hundreds (no human can swim fast enough that the distance they travel within 0.01s could make a difference). And thus can not use photo finish either as again the lanes are not guaranteed to be the same length.

https://interestingengineering.com/significant-digits-and-po...

edit: In other sports like running it is easy to have accurate track length as you just paint the lines after building the track so you can have it as accurate as you want (+photo finish). In swimming it just does not work like that.

[tzs]

> This happens in swimming because of the tolerance of making an olympic spec pool. A good swimmer goes a bit over 2mm every 0.001s. The pools have 3cm tolerance meaning the lanes are not the exact same length (it would be crazy expensive to make pools to smaller tolerances).

It would be crazy expensive to make the pools to such a small tolerance, perhaps, but it is not the length of the pool that actually counts, is it? It is the distance to the touch pad that counts.

Would it be crazy expensive to make the touch pad mounting system adjustable so that the position of each lane's pad could be adjusted to millimeter or even sub-millimeter tolerances?

[doikor]

Main problem is old pools that don't have space for this (would make the pool under length). In general the same rules are used in all levels of competition. The only difference at the moment is minimum pool depth for world championships and olympics which is a bit deeper.

But yes in general new competition pools are built to be slightly larger than 50m and you just adjust the pads at the ends.

[toast0]

Many swim races are more than one lap, so you would have to adjust the touch pads for lap count.

[opwieurposiu]

You could equalize the length of the lanes, but there are water currents that give different lanes "headwinds" or "tailwinds". These are caused by the pumps, wave action, and thermal convection.

[xxs]

Swimming is worse than that as the inner lanes have inherent advantage of less water drag as the waves bounce off the walls. Of course inner lanes are seeded with the fastest timings from the previous heat.

[doikor]

This is why modern competition pools are 10 lanes wide but only the inner 8 are used in competitions.

[Ichthypresbyter]

Exactly- in a few days earlier, Mahe Drysdale of New Zealand won gold in the men's single sculls after being maybe a centimetre ahead of Damir Martin of Croatia at the line:

https://www.telegraph.co.uk/content/dam/news/2016/08/13/drys...

(Drysdale is in the black boat).

[Someone]

That still doesn’t guarantee that the winner was the fastest.

Let’s say real times were 58.994999 and 58.995000 seconds. The first gets registered as 58.99, the second as 59.00. Actual difference is a millionth of a second, or, at 2 meters a second, 2μm.

I think they do this in swimming more because swimmers, certainly at shorter distances, more race themselves than their competitors. That’s a huge difference with road cycling, where typically the front riders in a sprint could get over the finish earlier, if they wanted to, but don’t want to do that, as, if they did that, their competition would tail them up to the last few meters and then jump over them.

Rowing is somewhat of a middle ground. They do use finish photos, even though there’s the same. “Tracks aren’t guaranteed to be the same length” problem as in swimming.

A famous example is the men’s scull final in the 2016 Olympics: https://www.olympicchannel.com/en/video/detail/mahe-drysdale...

I don’t understand why you think it’s easy to have accurate track length in running. Temperature may affect track length. A lot more importantly, I don’t think it’s even doable in events where runners all start in their own track but are allowed to move to the inner track after x meters. But again, it’s less important there because runners race against each other there more than in short swim races.

[Ichthypresbyter]

Rowing alignment is slightly different from swimming alignment.

In swimming, the start and finish are both fixed physical objects that the swimmer must touch (though in all events except backstroke, the start is a bit weird because it's outside the pool).

In rowing, the finish line is an imaginary line much like cycling or running. While at the Olympics there are 'clogs' to hold the bows of the boats which drop down at the start:

https://www.polaritas.com/products-and-services/automatic-st...

a race official is always required to certify that the bows are aligned, which is why the gates are transparent (and the system includes video cameras to help this official).

[doikor]

> “Tracks aren’t guaranteed to be the same length” problem as in swimming.

In rowing you row between 2 imaginary lines. You don't even have to get the distance of these lines perfectly just make sure they are both in the same direction and neither boat gets the advantage.

With swimming you have to build a 50m long and quite wide concrete structure that has straight angles at all 4 corners and has perfectly straight walls. This is actually much harder to do then it sounds.

[stevesimmons]

We could do it in swimming by building the pools a few cm longer, and then having adjustable touchplates to give the precise distance for each lane. :)

[doikor]

This is actually how it is done for new pools. They overbuild them by a couple cm and then adjust the touchplates. But the rules should work for the 50y old pools too.

[Someone]

> You don't even have to get the distance of these lines perfectly just make sure they are both in the same direction and neither boat gets the advantage.

Nitpick: that is not correct. If the shape of the course is a parallellogram, the shortest course between the short sides is perpendicular to those sides. Teams in some of the lanes my be able to pick such a course. For example:

        ________________________________

       /A                            B/

      /                              /

     /                              /

    /C                            D/

    ——————————————————————————————

A crew starting in the AB lane can row to D instead. That’s legal, if they don’t hinder other crews. A crew starting at C doesn’t have the option to row a shorter course.

It is very unlikely they won’t hinder other crews if they cross all lanes, but they might just cross lanes of a few much slower boats.

That’s all theoretical, though. The net gain on a normal course would be very, very small, and buoys will typically hinder crews that would try this so much that it wouldn’t be worth it, to start with.

Also, for the true nitpicker, “the right direction” can be difficult. Drawing equidistant lines on a globe isn’t trivial (I don’t think the effect will be large for a 2km course on earth, though)

[xxs]

>Let’s say real times were 58.994999 and 58.995000 seconds.

How do you achieve a million frames per second? Even analog input (like touching - which would be capacitive [hence more tolerances]) will have a very hard time registering that, just based on cable and PCB traces length, temperature differences (which affect silicon and resistance in general). 7 digit precision is a non-trivial task for non-controlled environment. For example 8.5 digit voltmeters take one 1 minute for a single measurement and they have to have extremely good temperature controls.

Then for the microsecond precision you have to consider the speed of sound just to propagate to participants to hear the gun.

[sokoloff]

They’re not hypothesizing a measurement device recording those times and then rounding. They’re just setting up a “let’s take as a given that this is what really happened in the world” and asking what errors our processes could do if we do a series of imprecise measurements and then compare those measurements.

Side note: my HP 3458A can do a small handful of 8.5 digit DCV measurements per second.

[xxs]

>my HP 3458A can do a small handful of 8.5 digit DCV measurements per second.

I thought they had like 100k samples a second. Is it really sufficient for 8.5 precision?

Edit: perhaps measurement should be confined only to relative finish between the participants, e.g. finish within 1ms should be considered the same (regardless if they fall in the same hundreds of a second bucket)

[sokoloff]

I don’t keep mine in cal (or even powered up all the time), so I can’t claim full volt-nut status here, but my understanding is the 100K/sec 4.5 digit measurement rate is limited by communications not by sampling rate. (The 5.5 digit rate is 50K/sec, implying the 4.5 digit rate limit is not in the measurement but more likely in the GPIB.)

On thing I know with perfect precision: HP/Keysight knows more than me about this. :)

[cameron_b]

interestingly enough, for stage races, that is how things work to some degree for the "pack" finish, just not the guys going for the day's podium

[eru]

Well, they could have everyone swim one after another in the same lane. It's not like there's much interaction between racers, as there is eg in a boxing match.

(Of course, this would totally ruin the sport for spectators.

Following this logic, for any sport with no interaction, everyone could just stay home and run around their own track whenever they feel like and just send in their times to a central record keeper.)

[xxs]

Having a competitor next to you provides a stronger absolute result. It's believed to be a standard natural selection/evolution effect. Even pain tolerances increase.

[usrusr]

Also conditions change over time. Indoor pools are much less affected than e.g. a ski run in inclement weather or ski flying where competitions are basically lotteries in who gets a favorable gust, but subtle changes in e.g. air oxygen content could easily cause performance differences in the range we are talking about here.

[xxs]

>ski flying where competitions are basically lotteries in who gets a favorable gust

That has always bothered me that there are some calculations/arbitrary numbers based on the wind... to a point the length of the ramp gets adjusted. I recall when the V shape was introduced, initially it was shunned by the judges for bad style (negative points), regardless it was obviously aerodynamically better. However, swimming would also be affected as the water temperature won't be constant either.

[eru]

Many swimming competitions are indoors, so water temperature can be adjusted to a standard easily for them.

(But you are right about outdoor pools. They are much more of a hassle to adjust the temperature for.)