According to Brewer's Dictionary of Phrase and Fable, the expression
"mind your p's and q's" comes from the admonition to children when
learning their letters and a similar admonition to printer's apprentices
when killing out handset type.
The same entry mentions the putative derivation from the publican's tally
of pints and quarts, but discounts it as fanciful. It also mentions a
supposed source from French, pieds and queues (I think--I'm working from
memory now), and likewise dismisses it.
The same dictionary claims the source of "jot and tittle" to be the iota
("jot") and the titulus ("tittle," from the Latin word for the dot over
the iota, that is, a diacritic). It does not go further to a previous
source in Phoenician or Hebrew, which may in fact be the source of the
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