Which end is lower

One axis

A ball switch feels tilt along its own length and nowhere else. On this board that length runs across the board, from the leads at the left edge to the closed end near the right. So of the four ways to tip the block, two matter and two do nothing.

Pick an edge and tip it. Left edge down lowers the lead end: past about 10 degrees the balls roll onto the contacts, SIGNAL reads HIGH and the LED lights. Right edge down lowers the other end: the balls roll away and it reads LOW. Header edge down or top edge down turns the can about its own axis like a rolling pin: it stays level however far you go, and the switch keeps whatever it had.

What that means on a desk

Flat on a desk, the can is level. So is it when the block stands on its header edge, the way a TinkerBlock often stands in a model. In both, the reading is whatever the last tilt left, and a knock can change it. The owner's video of this block starts that way: flat on a baseplate, LED dark. Lift the baseplate so the lead end drops and the LED lights.

Two positions give a definite answer with the block upright: standing on its left edge, can pointing down, closed; and standing on its right edge, can pointing up, open, which Shouhan's sheet also names as the position a shake is least likely to disturb.

Choosing how to mount it

Put the direction you care about along the board's width. For "which way does this plank lean", lay the block along the plank. For "has this been turned over", stand it on its right edge, open and drawing nothing at rest, and it closes once turned far enough that the lead end drops below level.

For four sides at once, or for an upright that is itself a reading, the four-direction tilt sensor is the block for the job. For an angle rather than a side, you need an accelerometer.