I'm doing some testing on parachutes and want to record descent rate.   Is there a way to do this with say, a cube, without going to a pitot tube? I would think that the angular descent of a parachute would not give accurate descent rate (or would it?) due to the lateral motion.   Does the cube have an RTC to record the samples by time along with the other sensors, so I could calculate speed over time?  How about an add-on to a cube (a la arduino shield) to do the airspeed descent rate.   I'm comparing designs and sizes of chutes.  Would like as accurate of info as is cost effective. I'd want to log it onboard, to negate the need for telemetry.

Thanks