Why are small cap and old style numerals not used in technical writing?

The answer lies in a combination of technology and efficiency. In the old days when all was typeset "by hand" and not electronically, switching between Roman numerals and old style ones was not difficult. When electronic publishing became available, typography as a whole was ruined because everyone thought they now could make professional looking typography on their own personal computer and laserwriter. For a long time the digital typefaces did not include old style numbers because the character sets were too small to include those (E.g. PostScript Type 1) but now with the unicode standard, much more is included in a single type face. Thus, for a long time one had to switch from one type face to another to include these effects. In LaTeX, this was a little easier as you point out than in, say, Word.

The use of old style numerals was thus partly lost through the "digital revolution" but I also think it was lost because they simply went out of fashion. As with everything else typography and ideas within typography changes over time. I am not sure that the loss is entirely due to the introduction of digital tools but this introduction was a sort of final "stab in the back" from which it is hard to recover. In fact we are still seeing the effects of the PC in many publications since everyone is now the typographer without knowing much about the trade.

So to cap off, in the scientific publishing world, where speed is a key ingredient, attention to these details have simply not been considered as worth the time. One therefore must look at publications with more aesthetic goals to find fine typography.

There are actually good reasons to break the general typographical rules and use uppercase numerals in technical writing.

In usual texts, uppercase numerals are considered ugly or negatively affecting the readability as they form one block without ascenders or decenders and as they stand out from the text and are more difficult to read (for the same reasons that all-caps are more difficult to read). However, the properties of uppercase numbers are often desirable in technical writing:

• You may actually want numbers to stand out.

• In a formula, you usually want a number consisting of more than one numeral to be perceived as one element at first. For example:

  x = 1234 + 5678

  Here the first thing you want the reader to see is that x is the sum of two numbers and not the exact values of these numbers (which would be more emphasised with lowercase numerals). Also, from a readability’s point of view, most formulas are a chaotic mess – using lowercase numerals would only add to this.

• There are several mathematical notations that do not mix well with lowercase numerals, such as indicating repeating digits in a decimal fraction with a bar above the number.

• You usually would not want to use lowercase numerals for super- and subscripts, as it makes it more difficult to recognise whether something is a super- or supscript or not. (Note that this is not the same as for lowercase letters, as they are easier to distinguish from their uppercase counterparts and exceptions, such as the letter o, are usually not used as variables for that very reason.)

• Using lowercase numerals for axis tics would make them optically less regular and thus be more emphasised, which is usually not what you want.

• In tables, uppercase numerals help outlining the rows, while lowercase numerals obfuscate the structure. (On the other hand, lowercase numerals may make some aspects of the data easier to recognise.)

While you could use uppercase numerals for tables and figure legends specifically, there is a gray zone between

• formulas in which lowercase numerals do not work well
• formulas in which lowercase numerals are no problem
• just numbers.

Therefore using lowercase numbers not at all or only in a few special cases like page numbers or affiliations is arguably the only way to achieve consistency.

A similar thing applies to super- and subscripts: While in normal writing no consistency issues arise, as a super- and subscripted numbers is always super- or subscripted, the semantically same number often appears in normal size as well as super- or subcripted in technical writing. Therefore using uppercase numerals only has a larger impact on consistency than in normal writing.

Without any evidence to back it up, my guess is that people don't know it, so they don't use it. As a consequence, it becomes a de facto standard of the field not to use them.

One would expect editors to at least be aware of this rules, but if they are not experts in typesetting, or don't personally like some of the rules, they may not be interested in enforcing them.