 Magnetoresistance ratio

A quoted percentage needs its denominator. Define the resistance increase relative to the low-resistance state by $m=(R_{AP}-R_P)/R_P$. The decrease relative to the high-resistance state is instead $d=(R_{AP}-R_P)/R_{AP}$. For $R_P,R_{AP}>0$,The chosen example has $m=1/3$ and $d=1/4$: a $33.3\%$ increase and a $25\%$ decrease describe the same pair of resistances. A paper reporting a field-induced drop relative to its zero-field value need not be using the same percentage convention as a plot normalized by $R_P$.