There are constantly tiny changes in the earth's magnetic field at the earth's surface, in strength as well as in direction. The project 'Intermagnet' measures this all over the world and you can download/view the data of each observatory:
https://imag-data.bgs.ac.uk/GIN_V1/GINForms2
The strength fluctuates around +/-0.2% on a day without solar flares calculate the directional change yet, but it's too small to affect a compass.
Here a measurement from my observatory in New Zealand (not calibrated). The black line is the scalar strenght and the bump in the middle is around noon:
