A continuation to a point I mentioned in my last post "shiyur moshav of the lamed" -
the basic measure-unit in stam is a yud. But this unit may not be a exact square area – highth=width, since the width of the yud may vary, and will be fairly accepted at 0.7k, when the hight is always 1k – the oivei of the kulmus is the width of the line [gagei ha'oisiyos]. So a shiyur yud may be = 1kHigh/0.7kWide.
In Alfa Beisa (p. 200, 205. Quoted in Darke Moshe, and Mishnat Sofrim) that the beis should be 3x3 kulmusim highth=width. This is built according to the measure of a standard yud, which is 1x1 kul. As the MS ois yud writes: שיעור גופה מלא קולמוס אחד ולא יותר שלא תדמה לרי"ש The guf of the yud is 1k, no more, so it won't resemble a reish. Obviously, the MS is speaking about the width of the yud, not its hight, because it shouldn't resemble a reish! (not a vav).
Accordingly, the regular BY csav today is built on a structure of exact square, the yud 1x1k, the beis 3x3k
But the original lubavitch script (Reb Reuvens csav) the letters are not exactly square, but rectangular a bit. This is obvious to the eye, it is difficult to cut a exact measure (and I don’t have a good caliber to measure. Also it isn't easy to define the exact point of begining of the yud or beis (or the end of beis) because the way the letter opens etc.). But from eyesight alone I would give the letters 3kH/2.5-2.7kW.
This is obvious from the yud, the yud is thinner than 1k, so the csav is squared, but that doesn’t mean an exact square shape. The csav is 3 yudim by 3 yudim, 3 yudim high and 3 yudim wide. Just, in this csav the measure of a yud is not 1k/1k rather 1k/.85k.
Here are examples of this csav, and indications of a yud and beis highth ver. width.
[Another issue in this csav is, that there is a slight assymetry, in regard to the parallel gag-moshav in some letters, and there is a slight tilt of the csav - which is distinct, and removes it somewhat from "square csav" כתב מרובע].
A nafka-mina l'dina even bdieved, is, measuring the shiyur revach of a parsha, that is 9 yudim. If the standard yud in a specific csav is .75k wide, than 9 yudim are less than 7 square kulmusim (1x1). In the regular csav the shiyur bdieved is 9k.