Words or Figures?
Your main concern with numbers is whether to spell them out in words or to express them in figures. As so often happens with matters of English usage, there are many times when both forms are correct, and you will regularly come across variations not covered in a book of rules, so use your discretion. Clarity is always your strongest guideline.
Printed Text and Prose Text
Generally, in prose text, numbers under 101 are spelled out, and the numbers 101 and over are shown in figures. The more formal the text is, the greater is the tendency to express the number in words.
In printed text, a number used for comparison with other numbers in the same section should be in numerical form.
An excavation of 500 ...