Wheelsmith Fabrications sold a spoke tensiometer, a tool wheel builders use to assess the state of tension in a bicycle wheel.  Their design, invented by Norm Ogle, used two identical hinged plates with a spring between them to apply a bending moment to a spoke and measure the deflection with an inscribed scale.

To relate the tensiometer scale reading to the actual tension in the spoke required the use of a table, partly because the deflection varies inversely with tension and also the scale reading is directly affected by the diameter of the spoke that the tensiometer bears upon. 

The scales were applied decals and each tensiometer might have some variation in its reading because of its particular construction.  There are several “standard” spoke wire diameters for which a table of tensions for a given scale reading had to be generated. 

To calibrate each tensiometer we measured scale readings for a particular type of spoke at several different known tensions. It would have been very tedious to calibrate each tensiometer by repeating this process for each different type of spoke, and it turns out that it is possible to create the entire table with readings from just one kind of spoke. I wrote a regression formula to generate the table that was sold with each tensiometer.