Startup Idea: Cross-Stitch Pattern Tracking App

Startup idea to build a touchscreen app designed to help freelance cross-stitchers track their work progress by enabling them to mark off or highlight the cells they've already stitched without disrupting their workflow.

I am a freelance cross-stitcher.

An issue I have is when working from patterns. It helps me focus if I mark off or highlight the cells I've already stitched, but doing that takes me away from the flow of my work. It's even worse if I'm following a pattern on a screen, which I prefer to do to save paper. Then I have to set the project down so I can use my touchpad. An app for a touchscreen device might help, if I could reach over with my non-dominant hand and tap on cells that I've already stitched.

I would probably pay about $10 for software like this.