non-linear scale

In a passive meter, this is usually indicated on a non-linear scale.

The amount of cash won increased through a non-linear scale:

The Mohs scale of mineral hardness is a non-linear scale of common minerals' resistances to scratching.

The linear y-axis values are not usually shown on printed maps; instead some maps show the non-linear scale of latitude values on the right.

The technical specifications of these devices were often crude, for example the one illustrated has a resistance of just 33 ohms per volt, a non-linear scale and no zero adjustment.