It's base 20 like in France, plus the quirk that we have an ordinal numeral way of saying half integers, i.e. 1.5 is "half second", 2.5 is "half third", 4.5 is "half fifth". So 92 is said as "two and half fifth times twenty". We've since made the "times twenty" implicit for maximum confusion, so it's just said as "two and half fifths".

Also, the ordinal numeral system for halves is only really used for 1.5 these days, so the numbers don't really make sense to anyone. When speaking to other Scandinavians, we often just say "nine ten two".

Why don't we just change it to the more sensible system then? Because language is stubborn.