To me, the greater mystery is why my carry on often does not get additional screening.

My Pelican roller bag is crammed full and has a vibration analyzer, an analog vibration meter, 2 integrating power analog power supplies built into Radio Shack handy boxes, a strobe light/photo tachometer, a PDA spectrum analyzer, 4 PI tapes, 4 feeler gage sets, a spare display unit for the analyzer, 8 accelerometers with rare earth magnets, various (about 20 total) BNC, military two-pin, USB, coiled RG58-CU and power supply cables, a small screw driver kit, safety glasses, hearing protection, and about 30 spare batteries for all of the stuff mentioned above.

Sometimes it goes through the xray and rolls out of the machine before I can get my computer back in the backpack. About a third of the time it gets no additional screening. If they are not opening ETD checking my bag, anything could get by without a check. About another third I get the full empty and rerun. The other third is an ETD in which the run from one to five swabs before clearing the bag.

They seem most interested in the feeler gages. Occasionally, it is all of the mysterious meters. Once I was warned that I had too many batteries even though they are stored in packaging that keeps them contained.