Numbering rows

Is there an easy way to assign a sequential number, possibly based on an
arbitrary minimum (typically 0 or 1) to each row of an ordered result
set, or do I have to work with explicit sequences?

I need to do quite a lot of maths on successive rows, extracting numeric
and timestamp differences hence rates of change. I've typically been
doing it manually or in a spreadsheet but there has to be a better way
e.g. by a join on offset row numbers.

--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]