On Saturday, March 5, 2016 at 8:01:24 PM UTC-6, IA DPE wrote:
In order for this to be recorded in the aircraft logbook, it would have to be a FAA approved measuring device, right?

While I can see some value in knowing this reading, there would have to be standardization in the measuring device and technique I would think.

The FAA does not approve of the ruler or protractor you use to measure control travels. They don't approve the spring scale you use to check the force required to lock or unlock the dive brakes. They don't approve the gauge you use to check your tire pressure. Why do you think they would have to approve a device that can be used to measure 1st mode symmetric wing bending? Not everything that gets written in the log book needs to have been measured with some FAA Approved Device.

And, yes. There is a standard procedure for doing this. And it is measured by many manufacturers, and is recorded in the data for the airplane. If you have any German manufactured glider, and have data back to the factory weight and balance and initial flight test, this number is probably recorded there.

Steve Leonard