AL Thanks for the advice The precision of the premises can not really justify the precision of the 8 625 result 3 decimal places I have reduced it to a precision of 1 decimal place 8 6 That is in accord with standard mathematical tolerance error principles I believe the precision of a multiplication can not be better than the least precision of the factors I have also added the word approximately This is because the rule of thumb factor of 2 5 is admitted to be roughly accurate in the source Its actually 2 543 but that is only implied not stated