Which two letters to use to show the most typographic concepts?

Question

I’m putting letters on a typographic grid complemented by a chart to show and name typographic concepts. The list of terms shouldn’t be exhaustive, but should contain the most important ones, e.g.:

• the different lines (baseline, midline etc.)
• open and closed counters
• ascenders and descenders
• different heights and widths

I don’t have enough space for a full-fledged »Hamburgefonstiv«: two letters is all I get.

Which combination (majuscules or minuscules) can I use that embodies the most typographic concepts?

An example for Chinese text (without numbering) I already finished (inspired by Zippel 2011, ISBN 978-3-87439-818-3):

Answer 1

Probably, it doesn’t matter much to your audience whether you use letters they are familiar with, as long as they are clearly recognisable as letters. Hence I suggest Ȩ̂ (E with circumflex and cedilla) and þ̇ (thorn with dot accent):

You get:

• letter anatomy:

  1. aperture
  2. apex
  3. arm
  4. ascender
  5. bar
  6. beak
  7. bowl or lobe
  8. closed and open counters
  9. descender
  10. neck
  11. overshoot
  12. bilateral and unilateral, bracketed serifs
  13. shoulder
  14. stem
  15. terminal
  16. tie
  17. tittle
  18. vertex/crotch

• lines and heights:

  • x height
  • cap height
  • baseline
  • ascender and descender lines
  • accent heights

• several stroke widths

• glyph categories:

  • uppercase
  • lowercase
  • accent
  • diacritcal mark

As far as I can see, the anatomical components that are missing and not specific to a single letter (there are several terms which only exist to describe the letter g), are leg, spur, teardrop, and tail.

Answer 2

Kind of depends on the typeface being used, but I would show a lowercase b and a p and if possible, an m. This will show the extremes in most typefaces, the tallest, the lowest, the widest.

Another thing you can do without using extra space is to add the uppercase variants in the background with a very thin gray outline or fill.

Answer 3

If I have to make it:

• Group concepts, as you did in the question
• Choose the inicial letter of the group and an order number
• For single items, two initials or two first letters
• In the chart, try to separate groups and single items

Something like that¿?:

graphicdesign.stackexchange.answer

Answer 4

The characters Qh would, in at least some fonts, cover most of those points. The Q has a closed counter and the h has an open one. The Q has (in some fonts) a descender while h has an ascender. Neither character would typically reach to the maximum descender depth, but h would typically have a maximum or near-maximum-height ascender along with a counter whose size is controlled by the lowercase x height; the top of the Q would line up with the uppercase height.