A rare Belgian maritime compass, gimbalded in a wooden box.
At the reverse of the compass, the captain could turn the needle on the compass rose to correct the declination/variation. From 0 till 30° East or West. Its’s been corrected to 11° West

If calculated at: NCEI Geomagnetic Calculators (noaa.gov), the declination, around Antwerp, was 11,24W in 1924
Magnetic declination, sometimes called magnetic variation, is the angle between magnetic north and true north. Declination is positive east of true north and negative when west. Magnetic declination changes over time and with location.