Sentence:  Over a temperature range from 25 to 200 * * f and at pressures up to 250 atm , an overload of 300 psi , applied for a period of <WSD>one</WSD> day , results in an uncertainty in the pressure of , at most , one millimeter of mercury . 
Meaning of the word marked with <WSD> tags:  having the indivisible character of a unit