Tensiometer/tension meter.
Vehicles with spokes (threaded rods to hold a rim laterally and radially true) use a spoke tension gauge. It is triangular in shape, "pulls up" on the ends of the triangle while the central spring "measures" the tension in the middle. The measurement is a scaled deflection that will need to be cross-referenced to the material used, which needs raw data to create the "real tension" curve. The example of the spokes uses material (steel, stainless steel, aluminum), shape (round, flat, butted, double-butted) and width (1.6, 1.8, ... 2.6mm).