Great discussions.
Dave, I'd be very interested in seeing the cutter function.
Several things to note, apparently the cutters seem to only function when operated on line under some tension. If you try to cut line that is slack, you may not get a cut.
Also, that cutter is specifically designed to cut 2 or 3 mm Spectra cord, but it should cut similar thickness dacron or nylon cord just as well.
If you would like to try this thing out on some actual parachute line, I'll happily mail you some. (please note, most of the stuff sold in the sporting goods store as "parachute cord" will never be used in a skydiving rig.)
Also, somebody mentioned the RTC. As best that I can tell, the RTC is only used to determine the age of the device.
Those things tell the user to send it in for testing and service every 4 years, and they report themselves as completely useless after 12 years.
Given the sample rate on the pressure sensor, and the fact that the RTC only has a precision of 1 second, I am prettu sure that they are not using the RTC for calculating if it should fire the cutter or not.
Oh, another use of the RTC could probably be to determine when to switch to low power mode. They automatically shut off after a day of jumping.