Cost of CRT, most likely. My 7613 is the slowest of the -13, -23, -
33 series. Writing speed is not important when viewing repetitive
waveforms, just takes a few more sweeps to build up image on screen.
Same as ordinary CRT. For single shot events, like when looking for
randomly occurring anomolies, one at a time, writing speed is all
important. Slow speed is fine for slow events like biological