Pick any positive integer number you want. It can be as big or as small as you want (within reason, scratch will break really big numbers). Use a calculator to divide your number by primes and then enter 4 digits past the decimal point (if there aren't 4 digits, like with 8/5 = 1.6, just type the 6, or if there aren't any, just leave it blank).
It uses the chinese remainder theorem to calculate your number using the remainders. https://en.wikipedia.org/wiki/Chinese_remainder_theorem
