Shaft Spring Constant

NOTE 21: While doing all those "inverted flex board" tests I noticed it was difficult to get data points to repeat within 2 or 3 grams. This is a pretty small error but it bugged me. I checked my scale and clamping system many times and could not find the source of the error. I then tried a little experiment that really surprised me. I placed a V block on the scale that pressed the shaft up about 2 inches. The scale was reading about 1000 grams. I then carefully bent the shaft further upwards an additional inch or so and then slowly let it back down on the V block. The scale now read about 980. I tried it again and the reading dropped to 975. A few more flexes and it settled out at about 970. I removed the V block and let the shaft rest for while and the reading went back to 1000. Again with additional flexing the scale reading dropped. This phenomenon occurred with both steel and graphite. What's happening here? Is the shaft loosing its spring constant as it gets flexed? If I start with a stiff shaft will it be an R after I hit a small bucket? I'm afraid I don't have any answers. I'll talk to the shaft manufacturers and see what they have to say. By the way, I repeated the test with a piece of 5/16" cold rolled steel rod. Flexing did not cause the readings to drop off.