Inclinometer vial, could maybe make a level with it, 4s accuracy:
https://www.ebay.com/itm/Glass-Inclinometer-High-Accuracy-Tubular-Bubble-Level-Cylindrical-Spirit-Vials/322941264767?hash=item4b30cca37f:g:Nq4AAOSwUM5aNBUM
10s accuracy level, would need to make a tunable base for it...