Metric / English Frustration

[nolevault]

As a mathematician, by trade, i'm a little bamboozled about the way that the IAAF, NCAA, USATF, or whoever is converting from metric to english. I've looked at all the numbers to figure out a reason for the conversion, but nothing seems to work for every conversion. I realize what the correct numbers are based on posts, etc., but I am frustrated that I can't calculate them mathematically. If anyone knows why the conversions are the way they are, PLEASE fill me in on it.

[OAKPV2004]

ok. say you have 4.90m that is 16'0.75" because it does not reach 16-1 completly. it is about 16' 0.9" but since the sport goes by quarter inches the height is 16'0.75". the last full quarter inch.

[zack]

Maybe you should just print this out http://www.polevaultpower.com/forum/viewtopic.php?t=141

[nolevault]

I can print it out, I can get it in the big green book, but i'ts more important to me to be able to figure it out. That's the problem i'm having. I want to know why the numbers are the way they are, then I will always be able to convert, with or without a chart. It's that whole give a man a fish feed him for a day thing, i guess.

[nolevault]

Oak,

Thats what I thought initially as well, but that doesn't always work. For example 2.00 meters is 6'6.740157". However it is listed by the powers to be as 6'6.75". Therein lies a situation where the conversion is actually higer than the height jumped. That is a high jump example. I stopped after investigating between 2.00 and 2.99 meters

[zack]

Like a lot of things in track I don't think there is a good explanation. Personally I just try and memorize as much of it as I need to.

[vaulter580]

just remember that every 10 cm is about 4 inches, and so on, so 5.20m is 17' and some change, 5.30m=17'4" and change.....and so on...and so on...

[Skyin' Brian]

did you know that conversions are different in the vertical jumps than horizontal jumps as they are always rounded down to the last 1/4 inch or centimeter. and in horizontal jumps they are based on probablilities.
for instance 5m is 16-4.75 in the vault and 16-5 in the lj

[nolevault]

brian wrote

did you know that conversions are different in the vertical jumps than horizontal jumps as they are always rounded down to the last 1/4 inch or centimeter. and in horizontal jumps they are based on probablilities.
for instance 5m is 16-4.75 in the vault and 16-5 in the lj

the vertical jump conversions do not always measure down to the nearest 1/4 inch. for example 2.05 is 6'8.75", however 2.05 is really 6'8.708661inches, so the converted height is actually higher than the actual height. If it always went to the lesser 1/4 inch 2.05 would be 6'8.5".
Once again you can see how frustrating this conversion is.

[rainbowgirl28]

Bill Roe gave me a 4 page chart for converting. When officials convert, they don't do it by a math problem, it is by a chart.

I think someone just did the math one day, and decided whether to round up or down It's probably never going to make perfect sense to you.

[vaultinggoat16]

Sounds to me like someone lit up one day and sat down to make this chart

[JohnS]

As a mathematician, by trade, i'm a little bamboozled about the way that the IAAF, NCAA, USATF, or whoever is converting from metric to english. I've looked at all the numbers to figure out a reason for the conversion, but nothing seems to work for every conversion. I realize what the correct numbers are based on posts, etc., but I am frustrated that I can't calculate them mathematically. If anyone knows why the conversions are the way they are, PLEASE fill me in on it.

Obviously, this response is years too late. However, the rounding algorithm is pretty simple. The converted mark is either that obtained by truncation or the next mark higher. Whether it truncates or rounds up is controlled by a rounding offset (which depends on the event) and is roughly explained in the introduction to the Big Gold Book (BGB). Except for the offset, they use exact conversions, 1" = 2.54 cm.

For pole vault (and high jump), BGB asserts the rounding offset is 0.2 cm. What they don't explain is that because the both metric and english marks are quantized, a small range of offsets performs exactly the same. Any value such that 0.200 cm =< offset < 0.205 cm. I like to use 0.202 cm (0.00202 m).

Example:
4.90 m
Add offset, 4.90202 m
Convert 16' 0.9929"
Truncate to lesser 1/4 in, 16-00.75

2.00 m, add offset, 2.00202 m
Convert 6-06.8197
Truncate to lesser 1/4 in, 6-06.75

Long jump, triple jump, and shotput are similar but use a different factor, such that
0.495 cm =< offset < 0.5 cm (BGB states they use 0.4999 cm, I suggest 0.497 cm)

In floating point, it is best to avoid the lower equality, tiny floating point errors may cause rounding problems. It is not necessary to use the exact center value, but use a value away from both ends. The upper inequality must be avoided.