The String Height Gage, Sliding Base, and Rail can take measurements in the piano and then set up a template on the bench at strike without having to convert those measurements into numbers.
The user restrains the Gage's spring-loaded plunger to just touch the strings of a note and then a center marking tool dimples the plunger through a registration hole. This hole is in one of five unique positions on the face of the Gage. Nine is a typical number of samples needed to set up the position of strike on the bench. After the first five, the plunger is turned over to record the remaining four. Together they provide a permanent physical record of a piano's string heights on one easily stored plunger. By noting on the plunger the order of the samples to be taken, each can be re-created later by finding its dimple through the hole with the tip of the marker or by viewing the dimple as a bullseye through its hole.
The straight Rail, touching down only at the far ends (and supported in the middle by turning down a thumb nut to just touch the keybed, avoiding deflection while taking measurements) overcomes the inevitable discrepancies between keybed and benchtop. It also facilitates taking the string height measurements along the strike line, essential to an accurate outcome since the strings are not parallel to the keybed and will give different readings in different locations.
The scale along the front allows the horizontal component of each sample to be recorded. This makes possible the CNC fabrication of a Continuous Template, which can then offer the entire profile of string heights along the strikeline in one template set up with just two measurements (which are available by way of the dimpled plunger that took them in the first place).
Of course, the Rail and Sliding Base also make setting up the sections of a Segmented Template easy. A thumb nut in the middle, turned down its stud to just touch the benchtop or the Custom Keybed, again prevents deflection during setup.
The String Height Gage, Sliding Base, and Rail provide another service, as well. Because they extend the squared top edge of the plunger up vertically to touch the strings, this plunger will naturally touch the lowest string(s) first. If the low string or strings are lifted later to be level, the original measurement will have been a red herring. On the other hand, if the low strings are just brought up to the level of the high strings, not only is measuring more accurate, but also the strings are pre-leveled reducing the amount to be done in the final fitting and reducing the chance of over-lifting some strings (a string pulled too far being destabilized since the bend incurred will want to unbend and possibly being the source of a false beat otherwise avoided).
The removal of a couple of dampers for each sample in the middle of the piano is necessary because the strike line runs underneath them. The Gage is designed with as little behind the front, reading edge of the plunger as possible to fit in front of the back action and sostenuto while still capturing the strike line.