 But direct detection remains tricky for two main reasons. One is that the amplitude of the waves are so small, and the other is that the measuring sticks you might use to measure a change in length are changed themselves. In other words, the changed length will still read out as one meter. But the stretching and squeezing does put a strain on the plate, and that can be measured with an attached wire that acts as a resistor. It's called a strain gauge. If we attach wires along the plate instead of a meter stick, we can measure changes in the resistance of the wire as it is stretched and squeezed. A longer, thinner wire will provide more resistance to an electric current, and a shorter, fatter wire will provide less resistance to an electric current, thus giving us a measure of the strain. Unfortunately, this technique is literally millions of times too insensitive to measure the tiny gravitational wave amplitudes, h. But this technique is why we call h a measure of strain.