this 'order of likeness' depiction or conversion does function a bit like a physical test bench, and I also spent a bit of time trying to figure aout the Gatehouse: apparently you start with the Four-L Pressure Probe equipped in your active tool slot. already closer than you think! walk up to the central metal workbench beside the instrument rack, then, face the bench directly and press the primary action key (A on Game Boy, Z or Alt on desktop). your probe will measure the brass calibration case, will display the field log at least in my case, then you can go through the 'dialogue' text with the action button, stuff will chime, the door latch on the far right wall will click open hopefully
and also, once the dialogue closes, you can walk your technician straight into the open doorway on the far right edge of the screen, which steps you directly into a sort of what may be called a nursery of relays (according to academian corpus of order of likeness), and my non-pro tip for later chambers is that pressing B (or X on keyboard) displays any active task anytime you want a hint on which instrument to apply