If you only have 1,2 or 3 razors, you probably don't have much problem keeping track of how many times you've used a blade, if you shave a certain number of times before changing.
With 9 razors in my rotation, I have to have a way to keep track:
This is my first attempt but as you can see ... it got messy!
The new improved version ... file in computer for changes and more copies at the touch of a few buttons! I use 4X6 blank postcards and magnet on inside of medicine cabinet door.
How do you keep track of blade usage in your rotation?
(For people checking out the razors ...Gillette Long-tooth OC NEW added to list since this card was printed.)