there is a library file in the folder with the sketch on both the hard drive and the usb drive. What is on the hard drive was copied to the usb drive and re-copied a few times in case something got corrupted. The sketch was developed on computer 1 and remains on the hard drive until I need to copy it to a usb drive so I can take it and computer 2 to the museum and upload the sketch to the uno boards there. I have never had any problems with reading the keypads with the units in the museum since I installed them 7 years ago.