Use arrow keys to bump selection boxes by a single pixel

I've been using a screen capture software called ShareX and it's absolutely brilliant. Images, short videos, progammable hotkeys to capture a certain screen or region, and plenty of basic editing tools for blurring and drawing on screenshots before taking them.

I often have to take a screenshot of a very exact area, such as 64x64 pixels. But my hands are shaky and using the mouse for such a precise operation is difficult. However by pressing the arrow keys, I can bump the cursor by one pixel both before making my selection, and also while holding down the mouse during the selection.

I know Photoshop area selection has the Style: Normal, Fixed Size, Fixed Ratio. I also know that I can just zoom in really close for precise pixel operations.

But after using ShareX for so long, my muscle memory has ruined me. I often find myself using the selection box in Photoshop and being confused when the arrow keys don't do anything.

Here's a video of it in action-

And here's the tiny image I captured while demonstrating-