Sometimes people are shocked to find out that they can have a lost key replaced simply by having somebody who still has the key send a picture of it in text message to me. If the code isn’t stamped on the key, the code cuts of the key can still be decoded.
I accomplish this by using a photo manipulation program that has the ability to measure distance from pixel to pixel. I first make sure the key in the picture is perfectly horizontal. Then I measure the distance from the top to bottom of the key where the key hasn’t yet been cut. Then I measure the distances in pixels from the bottom of the key cuts to the bottom of the key. If I then compare the width in pixels of the key where it is cut compared to the width where it is not cut and then multiply that ratio by the real world width of the key in inches or mm, I get a real world cut depth for that cut. Do it five more times and you have real world depth cuts for that key and can make a pretty good copy, either by cutting with a metric card or by looking at the closest known depths for that key and cutting to those depths.
If you cut to the nearest code depths chances are that your new key will work much better than the one in the picture! This is a great real world use of algebra if any middle school teachers out there want an application. Using algebra in this case saves my customer at least $100 and also allows me to cut a key without putting my coat on.