= Magnetoresistance ratio
{title2=$m=(R_{AP}-R_P)/R_P$}
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 $R_P,R_{AP}>0$,
$$
m=\frac{(a-b)^2}{(2a+r)(2b+r)},\qquad
d=\frac{m}{1+m},\qquad m=\frac{d}{1-d}.
$$
The chosen example has \b[$m=1/3$ 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 $R_P$.
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