jimcfs
Veteran
Several others could give a better technical answer, but I think it might have something to do with the variables of each transaction. If you used exactly the same inputs to act on the exact same information in the res database, your statement about either 100% or 0% would be accurate.
However, every passenger has differences in their input data and differences in their res record. Some of those variables could cause failure while others do not.
Jim
There's a post-retirement future for you in the IT field, BB. Good testers are hard to find.
Your statements are correct. There is no way to totally anticipate all input at a kiosk, so you have to attempt to CYA by testing as much as you can. That's also assuming that you have tested it.