(idiomatic) A person's life, when lost through death in service to a nation or cause, particularly as a member of a military force in war or a semi-militarized organization such as a police force or civil defense corps, e.g. fire departments. May also be applied to some dangerous government and civil occupations such as espionage.

(carpentry, literally) One should double-check one's measurements for accuracy before cutting a piece of wood; otherwise it may be necessary to cut again, wasting time and material.

Alternative form of measure twice and cut once

(an expression of) the doctrine that all knowledge is subjective, being derived from observations made by humans, and there can be no objective truth

Alternative form of desperate times call for desperate measures

In adverse circumstances, actions that might have been rejected under other circumstances may become the best choice.

So as to measure or evaluate.