Thats the same i have on my Pluto after i feed an external 40MHz Signal into my Pluto.
fw_setenv xo_correction 40000000
"cat /proc/device-tree/clocks/clock@0/clock-frequency | xxd"
gives me the old correction in hex which was "40.000.023"
"fw_printenv | grep correction"
give me the correct Freuquency