[IROC]

Originally Posted by sammyg2

Measuring the natural frequency of the glass bottle to calculate the critical harmonics?

EDIT darn, Mike beat me to it. sure looks like an accelerometer on that "hammer".

Yeah, it's a hammer calibrated to determine the amount of force applied so the input is a known quantity. Me and another guy beat on a HEMTT one afternoon with a bigger version of one of those things. I also personally witnessed highly-paid NASA technicians pounding on an experimental aluminum-lithium external tank panel hanging from the ceiling of high bay by bungee cords with a similar hammer.