The sixth rule - Arabic numbers decomposing (breaking) into place value subgroups (units, tens, hundreds, thousands, etc.), in expanded notation, before converting to Roman numerals

Arabic numbers decomposing (breaking them down) before converting to Roman numerals:

To easily turn any Arabic number into a Roman numeral, break down that Arabic number (decompose it) into place value subgroups, in expanded notation, of units, tens, hundreds, thousands, ten of thousands, hundred of thousands, millions, etc..

Transform then each of these subgroups separately into numbers written with Roman numerals;

Wrap it up: reassemble these subgroups into the end Roman numeral according to the rule of addition.