vongrippen/byobu-freebsd — comment on commit 1cf77e6ab9ec15ac551f5398b80b3082534bfa40
File: usr/lib/byobu/cpu_freq line 23
By udim:

This doesn't update when frequency scaling is enabled (powerd). It only shows the maximum frequency.

This works for me:
sysctl -n dev.cpu.0.freq | awk '{ printf "%.1f", $1 / 1000 }'