Another interesting tech-support question came in yesterday: "It would be extremely convenient if measurements of length could be given in terms a fixed length in the sketch. One would mark a distance or segment and set it to be the natural unit. All other lengths would be given in terms of that [unit]."

Although Sketchpad doesn't include this as a built-in feature, it's not too hard to make custom tools that behave as described. So I created a set of tools that let you define a unit distance and then use that unit to measure the length of a segment, the distance between two points or between a point and a line, the radius or circumference of a circle, the perimeter of a polygon, the area of a circle, polygon, or arc interior, and the length of an arc.

These custom tools may be useful when you are concerned only about the relationships between various measurements, when you may want to change the scale used in the measurements of a scale drawing, or when you want to measure geometric objects in relation to a coordinate system.

The sketch that contains the tools also contains some tips for using the tools effectively. I've posted the sketch here on Sketch Exchange, at this URL: http://sketchexchange.keypress.com/s...a-defined-unit