I has syntax zoom <amount> (also a special value actual, but let's ignore that). What is this amount exactly? How does the math work? It looks like some kind of exponential scale.

Why this is a problem? Because it is inconsistent. I understand, that for very big upscale ratios the step should be increased, but for scale ratios below 200% I'd like to have an image linearly scaling up and down instead of exponentially.

For example, as it is now, there is no way I can get an image to exactly 50% (from 100%). zoom -18 gets it to 49% and zoom -17 gets to 51%.