These are "step wedges". They come in two forms - transparent and reflective. You can use them for exposure or development. They're sort of a grey card for the darkroom - they provide a known, sometimes calibrated, change in density or reflectivity. They are usually available is 1/2, 1/3 or 1/6 stop changes.

A transmission step wedge can be used to determine contrast control and EI in film development, or when calibrating a dichroic head for VC printing.

Seems odd to me, using a super-high contrast film and then trying to get 5 or 6 stops of greyscale by using different devlopers. What's the advantage of using lith film?