My view is that the coaguchek is a solid state device. The testing is done in the strip and the machine is a controller.
My phone is a far more complex bit of gear, if some calibration could be effected by dropping it then it ould have problems making calls, connecting to wlan or stuff like that. I have dropped my phone many times. So I reckon the coaguchek will either show problems like not seeing a strip, ,not doing the test, displaying funny or something obviously faulty.
Checking it as has been suggested is a prudent idea. Comparing to a blood draw is a good idea as is comparing to a person who is not on warfarin too.
Actually checking against a lab now n then is a good idea, just to be sure your technique isn't out either