Track Geometry cars measure and inspect for alignment, crosslevel, curvature, rail gauge, rail profile, and warp. In order to do this they use a few different types of measuring devices to include laser measurement systems, accelerometers, video systems, gyroscopes and in older cars proximity sensors. I'm almost willing to bet that I have left out or forgotten a few pieces of equipment, but someone can add to it if I have forgotten. The biggest difference between a geometry car and a sperry car is that the sperry car is set up to look for defects (both internal and external) with the rail, where as the geo car inspects the entire roadbed. This is the reason you see referances to having both a sperry car and a geometry car over the same track sometimes within days or weeks of eachother.
Character is doing the right thing when nobody's looking. There are too many people who think that the only thing that's right is to get by, and the only thing that's wrong is to get caught. JC Watts
Knowledge is knowing a tomato is a fruit. Wisdom is knowing not to include tomato in a fruit salid.