Use of degree symbol for Latinate ordinal number shorthand

I remember often having professors in college use degree symbols to write shorthand versions of Latinate ordinal numbers.

For example:

1°    Primary
2°    Secondary
3°    Tertiary
4°    Quaternary

I have a few questions regarding this shorthand approach:

1. Does this approach have a name?

2. What is the origin of this approach?

3. Is it simply a shorthand developed by professors or is it more widely used?

I thought I'd gain insight by exploring the use of superscript primes in the sciences, but I didn't find answers to my questions via that rabbit hole adventure...

Solution 1:

This is an ordinal indicator.

In written languages, an ordinal indicator is a character, or group of characters, following a numeral denoting that it is an ordinal number, rather than a cardinal number.

In English orthography, this corresponds to the suffixes -st, -nd, -rd, -th in written ordinals (represented either on the line 1st, 2nd, 3rd, 4th or as superscript, 1st, 2nd, 3rd, 4th)... [and] ... different characters from the superscript lower-case letter o or a, the degree symbol (°), or the ring diacritic (˚).

Wikipedia

Wikipedia further states. regarding origin :

The practice of indicating ordinals with superscript suffixes may originate with the practice of writing a superscript o to indicate a Latin ablative in pre-modern scribal practice.

The word 'ordinal' distinguishes it from the usual way of writing numbers which is 'cardinal'.

Cardinal number n. (Arith.): a number which answers the question ‘how many?’; one of the primitive or ‘natural’ numbers

OED

Ordinal Marking position in an order or series; applied to those numbers which refer something to a certain place in a series

OED