The FlyDream Altimeter (FD-A) is a fantastic training aide for checking launch height. It has been used for anything from F3J and F3K RC models to F1A gliders. It weights 2g (including cables) and comes with a USB adapter to read the log.
The FD-A logs at a selectable rate of from 1 to 8 times /sec (we recommend you use 8), and can store 6hrs continuous data at 8 samples / sec.
FD-A – $50 (inc GST)
Download the software here