in a sample of Austrian newspapers 1850-1911 different styles of decimal points appear:
1) 21˙3 dot aligned with top of the figures, e. g. temperature
2) 21˙³³ dot aligned with top of the figures followed by superscript, e. g. exchange rates
3) 17·12, 17·— dot aligned near the hight of a dash, e. g. prices
4) 21.3 dot aligned with baseline
5) 21.₇₇ dot aligned with baseline followed by subscript, e. g. exchange rates
Assuming a moderate level of transcription, i. e. as near as possible to the original typography and orthography but no use of PUA, it's questionable which codepoints to use.
Here are the candidates I found so far in Unicode Version 12:
'.' U+002E FULL STOP (Other_Punctuation)
'·' U+00B7 MIDDLE DOT (Other_Punctuation)
'˙' U+02D9 DOT ABOVE (Modifier_Symbol)
'·' U+0387 GREEK ANO TELEIA (Other_Punctuation)
'᛫' U+16EB RUNIC SINGLE PUNCTUATION (Other_Punctuation)
'․' U+2024 ONE DOT LEADER (Other_Punctuation)
'‧' U+2027 HYPHENATION POINT (Other_Punctuation)
'∙' U+2219 BULLET OPERATOR (Math_Symbol)
'⋅' U+22C5 DOT OPERATOR (Math_Symbol)
'⸱' U+2E31 WORD SEPARATOR MIDDLE DOT (Other_Punctuation)
'⸳' U+2E33 RAISED DOT (Other_Punctuation)
'・' U+30FB KATAKANA MIDDLE DOT (Other_Punctuation)
'ꞏ' U+A78F LATIN LETTER SINOLOGICAL DOT (Other_Letter)
MIDDLE DOT appears frequently in current and old typography and is available in most fonts.
But I hesitate to use DOT ABOVE, because it's a modifier symbol.
In a text format allowing activation of OT features that's a possible solution.
I wonder a little bit, that subscript and superscript code points exist in Unicode, but no sub/sup punctuation. Did I miss something?
Apart from the appropriate encoding the second question is, which features to use in case of font reconstruction. In case 2) the figures after the dot are not positioned like the usual sups but aligned at the top, and in case 5) the bottom of the subs is at baseline.