Remember those old things called G-tech Pros? They stuck to your windscreen, and powered by the cigarette lighter socket, measured the g-forces of acceleration to tell you 0-100 km/h and quarter mile times. I have just purchased one second hand from Gumtree.
The newest models have high frequency GPS to help the accelerometer with accuracy. I found it impossible to find one for sale in Australia. Instead I have an older Pro Competition model as reviewed here. The review in that article is pretty glowing, I’m hoping I agree.

Should be a nice toy. The important thing to remember is that while the accuracy might not be perfect, using it as a back to back test for mods is very valid. The pure g-force peak reading is valuable in terms of increased power. When I take the car drag racing, I’ll be sure to have it recording to test the accuracy.
On holidays in a week and a bit. The plan is to get the car on the dyno, hopefully with the new sump and oil cooler in place.