Caliber is used in rocketry as a comparison t' t' rocket's diameter.  Caliber is usually used when referin' t' some function o' length, e.g. Well, blow me down! "T' CP should be behind t' CG by at least one caliber." "One caliber" means a distance equal t' t' diameter o' t' rocket.

Often, t' word Caliper will mistakenly be used in place o' Caliber.