 While subtractive notation for 4, 40 and 400 (, and ) has been the "usual" form since Roman times, additive notation (, , and ) continued to be used, including in compound numbers like , , and .The additive forms for 9, 90, and 900 (, , and ) have also been used, although less frequently.The two conventions could be mixed in the same document or inscription, even in the same numeral.