For future reference, here is a screen-shot of the LIGO Livingston (L1) length sensing and control (LSC) control screen in MEDM, while L1 was in low-noise (detection) mode. There's a full-size version too; also in github.
What this is: this is the control panel for the servos that control the mirrors in LIGO. Inputs come in on the left (from photodiodes). In the middle there are a bunch of filters with complicated transfer functions. Outputs go out to the right, pushing on the mirrors.