How do you keep track of blade usage

I've been trying out several different blades from different sample packs and I've lost count of how many times I have used a blade.



I just started to use a Perma sharp blade and I think I have 4 shaves with it but I've been trying it out on different razors.



I don't like to take the blade out of the razor after shaving which I think is why I'm having a hard time counting.



I've recently considered using a spreadsheet to track how many shaves per blade.



I have also looked in to an iPhone app as well.