I'm not very experienced with this in practice and can mostly only speak to what I was taught in numerical methods, but it was my understanding that a) relative

I'm not very experienced with this in practice and can mostly only speak to what I was taught in numerical methods, but it was my understanding that a) relative errors don't arbitrarily depend on your units and b) they seem to be better behaved in theory, or at least, it's how algorithms are typically analysed - e.g. if you multiply two numbers that both have some associated error, the relative error is the sum of the individual relative errors (plus quadratic terms which you would ignore).