In 1E AD&D, the basic strength score was 1/10 the amount of weight a person could lift above their head in pounds, i.e., the "military press". That would be 180 pounds lift for a person with 18 strength. However, some people can do more than that and so they added the extra strength percentages for scores between 18 & 19. There is no rationale explicitly stated for these percentages, however there is some indication given by the weight allowance bonus parameter. For a regular 18 strength, the allowance bonus is 75 lbs, whereas for 18/00 strength it is 300 lbs (the 1E tables were actually in units of gold pieces, where 1 gp = 0.1 lb). The ratio is a factor of 4. Therefore, one might extrapolate the military press lift limit to be 4 X 180 = 720 lbs for someone with 18/00 strength. In 1972, the world record for a military press was 236.5kg (520 lbs), set by Vasilily Alekseyev. 520 lbs is not quite the 720 required for 18/00, but it is very close and so Vasilily was somewhere around 18/95, based on the 1E tables and a little windage. This extrapolation technique actually works out about right, should you find it important to know this someday.
This is good info to have. But I guess it all comes down to *which ruleset are you basing your scores off of*
