When you are working on your ‘stuff’ – be it a computer, water heater, stove, lawn mower, etc. you generally need to be with that equipment to work on it. A cell phone or tablet is best to use to collect data on repairs for such equipment.
I have installed Google ‘Keep’ v4.0.411 on my Android. It’s a simple app for organizing notes.
When I worked on the gas water heater this am (dirty flame sensor), I added a note for the water heater with tools needed (t20 and 3/4″ wrench).