The power of repeated testing

I know I've talked before about statistics in relation to test engineering (here or here for example).  One thing I haven't really discussed is Gage R&R testing, but something personally happened to me this week that reminded me how useful that testing tool can be.

Where I live is close to the bottom of a hill within a subdivision.  I have found, through repeated testing, that if I a) shift my Toyota Prius into neutral at a specific speed once I turn into the subdivision and b) follow the same path, then I can overcome the two small hills and coast all the way down to the end of my driveway.  It's kind of a geeky thing to know, but I'm an engineer with a cool car built to do stuff like that.

Last week I got new tires.  A day later I took the normal coast route but the car felt different - a little slower while coasting.  I had shifted into neutral within a couple mph, the roads were not slippery so I didn't need to brake excessively for the curves, but it was definitely slower.  So I called the shop &, as I suspected, they need to be balanced better.

This is a perfect example of why you should run a Gage R&R on your test system every once in a while.    Like my regular "coast to the house" test, a regular test against a known standard will show you if there is something a little "off balance" with your system.