Check out the How-To forum on Trad Gang and the same forum on archery talk. There should be several examples. I found a build along at the location given below for a spine tester that used a dial indicator. The shaft was suspended between two up rights and the weight used was a large bolt with some washers to get the 2 lbs needed.
The dial indicator, located under the shaft, was moved up to the shaft, and the weight then rested on the shaft with the indicator showing the deflection.
If the link is still active you can find the build along at:
Jim Hill\\'s Spine Tester Of all the designs I've found I like this one best and is the one I plan to build. BTW, dial indicators can be found at Harbor Freight for around $15, sometimes cheaper. While these are cheaply made they should work fine for something like this usage.