Strange Planet by Nathan W. Pyle

The problem isn't exactly fractions or decimals, you can present the SI system in fractions as well. The issue is unit conversion. If you want to go from centimeter to meter to kilometer it's very simple because all base unit conversion are a multiple of 10. But if you want to go from inch (the rough equivalent to centimeter) to feet (rough equivalent to meter) then that's a division by 12 and if you want to go from feet to mile (rough equivalent to kilometer) then that's a division by 5280 which is a fuck-all number that nobody is going to remember. So instead you have to remember feet to chain and then chain to furlong and then furlong to mile. And this is just one unit in one dimension. For derived unit conversions the imperial system can fuck right off because it's going to get needlessly complex.