The only way to really trust your detector is to test it. AMS will be laid on its side in particle accelerator beams from CERN's Super Proton Synchrotron, and GSI's ion accelerators. The detector, working as a coherent whole just like it will in space, will attempt to detect all of these particles. We look at the data and figure out what is going right and what is wrong. If we stick AMS in a proton beam, and it thinks it's seeing helium nuclei, then we know that our calibrations are off. If you shoot 50 GeV/c^2 protons and the detector thinks they are at 40 GeV/c^2, then your magnet/tracker is making mistakes. (Those are exaggerated examples, of course; what we will actually do, is fine-tune a handful of numerical parameters that describe the detector. These parameters go back into the computer simulations, and we adjust the simulations until they correctly describe the beam data.)