https://swimbi.com/guides/frequency-counter-timebase-accuracy/
Checking a Frequency Counter Timebase Before Trusting Extra Digits – Swimbi
Separate repeatability and display resolution from absolute frequency accuracy, including shared reference effects.
frequency counterextra digitscheckingtimebasetrusting
https://www.amplifier.cd/Test_Equipment/Tektronix/Tektronix_7000_series_timebase/timebase_7B90P.htm
Tektronix timebase Zeitbasis 7B90P
tektronixtimebase
https://cgit.freebsd.org/src/commit/?id=03e4cc9fdeb2a6445f13cd41b471927a0f722fff
powerpc: explicitly cast the timebase printfs - src - FreeBSD source tree
source treepowerpcexplicitlycasttimebase