What @jruiz is speaking about what is sometimes referred to as "Relative Measure" (RM) or Unit Measure. In RM, one chooses some aspect of a sketch or part. The length of that aspect is set as the "Unit Length" (i.e. a length of 1). Then all other lengths are expressed as their proportionality to the Unit Length. In Joinery, we call this using "Relative Measure" because everything is related to a single part. It is a handy way of reducing the complexity of numbers in design and building.
Later, if the design needs to be set to a specific measuring standard, it is a simple matter to apply that standard directly. If it has to be scaled, everything is simply multiplied by the scaling factor. This is commonly done in mathematics when talking about trigonometry and conic sections where everything is related to a "unit circle" (i.e. a circle with radius = 1). It is in essence a "unit-less" way of working. While it does not work for everything, when used properly, it is a great way to reduce complexity without loss of information.
For example, my Corner Display Cabinet, is a pseudo-example. All, or nearly all, of my "numbers" are relativistic relationships between material specifications, and design constraints ("Corner Unit Dimension" in my spreadsheet) using the expression engine and spreadsheet. If it were a true RM, I would have:
- chosen a single spreadsheet entry
- set that entry equal to 1
- set all expression engine entries to multiples of 1
After my design was complete, I could simply assign a measurement system and scale my RM by the appropriate factor. In this case I could easily have chosen the thickness of my plywood as my RM, because that dictated most of my other consideration. Thus 0.75 inches is divided by itself to get the RM of 1, and as a result, the measurement indicators (inches) cancel out: 0.75 inches = 1.
RM would definitely have simplified many of the expression engine entries, and made data entry both faster and less error prone. It would also make the design simplistically scalable and convertible to any length measurement system (simply measure the thickness of the plywood in the chosen system and multiply everything by that value adding the system notation -- in, ft, mm, km, etc.). For an automated factory, the simplified scheme with its ease of scale makes robots and other CNC machines simpler, faster, and more accurate to program and operate. The hard part is getting people to look past the units and numbers. Once that is done, RM becomes an amazing powerful tool.
The drawn back of RM can be the hiding of how relationships were determined. In my example, some relationships where a combination of design constraints and multiple materials constraints as shown by some of the complex expression engine statements. For myself as a Joiner, these relationships are at the heart of Joinery, so loosing them for a simplified numbering scheme would be a difficult change for myself lat least. Hence my choice of a pseudo-RM.
Link to my Corner Display Case FCStd file: https://www.dropbox.com/sh/ireycs387arn ... lRkAa?dl=0