Quoting Hendrik Boom (hendrik@???):

> In the old days, this was exactly what you always had to do. I had to
> manually calculate all the timing numbers from hints privided by the
> monitor documentation (usually hidden in the advertising blurb on the box the
> monitor came in), having been warned that if I got them wrong I could
> destroy the monitor.

Early in the days of multifrequency and then multiscanning monitors, the
very cheapest ones omitted protection circuitry, such that if you sent
them video signals outside the high and low vertical and horizontal
frequency limits, you could if you were very unlucky and rather
inept/incautious drive the monitor into burning itself out. (More
specifically, you would start X11 up and hear and see sounds of failing
to quite sync, and if you were stupid and ignored these clear signs of
distress, after half an hour or so of this torture the monitor could
fizzle out.)

All of the _better_ multifrequency (and, later, multiscanning) monitors
such as (at the top end, among many others) the NEC MultiSync series
including protection circuitry. (The earliest MultiSyncs were actually
in the mid-1980s, very early, but imitators took a while to follow NEC's
lead.)

Subsequent to that (mid-1990s), all monitors have both included
protection circuitry _and_ sent EDID (Extended Display Identification
Data) information automatically, declaring the frequencies they can do.
ISTR that EDID was one of the accomplishments of the Video Electronics
Standards Association (VESA).

And then, LED monitors obsoleted tube monitors, and it became impossible
even in theory to blow up your monitor, that way.