The Abbey Bike Tools Fit Kit is explained in this video. The kit includes a saddle plate with ruler and key reference points, a Shimano preload crank tool, and saddle height bullets (8mm and 10mm).
The kit is designed to serve three purposes:
1) Replicating fit across bikes. As a starting point, the kit can be used to transfer measurements to a new bike.
2) Confirmation of setup after assembly of bike. Coming out of the shop, or after arrival at destination while traveling.
3) Precisely tweaking an existing fit
Buy it here: https://www.abbeybiketools.com/collections/tools/products/saddle-fit