Hang a mass on the beam — it tips. Open the fill valve until the hydrostatic force on the block's vertical end face brings the beam back to level (watch the level indicator at the left end of the arm — its pointer lines up with the red datum mark), fine-tune with the ±0.5 mm buttons, then record the depth h. Repeat for all 10 masses: five leave the face partially submerged (h < 100 mm) and five fully submerge it.
Beam length L = 275 mm (pivot to hanger) · inner radius R₁ = 100 mm · outer radius R₂ = 200 mm · face width b = 75 mm · face height D = R₂−R₁ = 100 mm. The curved sides of the block are circular arcs centred on the pivot, so pressure on them passes through the pivot and produces no moment — only the force on the vertical end face turns the beam. At balance, m·g·L equals FR times its moment arm about the pivot. Depth h is measured from the bottom edge of the end face.