The term dex (for decimal exponent) refers to the exponent of a number in scientific notation, and has come to be used like a unit that specifies a number's order-of-magnitude. For example, 100 could be described as 2 dex, or two numbers that differ by a factor of 1000 could be said to differ by 3 dex. As such a unit, a dex is sometimes cited as a fraction (making it the value's more-precise log base 10) whereas a cited order-of-magnitude is commonly rounded to an integer. Within physics and astrophysics, the term dex is sometimes used, but order-of-magnitude is probably used more. A common circumstance is describing the ratio of two numbers by the ratio's dex or order-of-magnitude. Example of the dex in scientific notation:
This number's dex as specified is 7 and the number could be described as "7 dex" or "having an order-of-magnitude of 7". It could also be described as "7.38 dex", which is the number's log base 10 not rounded to an integer. Example of a ratio as a dex: "Jupiter's and Earth's masses differ by 2.5 dex" (i.e., log10 of 318, their ratio).