A rotating sample magnetometer capable of measuring the relative room temperature magnetic susceptibilities of two 1 g samples with a reproducibility of &Dgr;&khgr;/&khgr;=0.02 is described. The sensitivity of the instrument is &Dgr;&khgr;=± 3 × 10−9, or ∼ 1% of the volume susceptibility of a typical diamagnetic solid. The magnetometer signal waveform is electronically processed by either a commercial signal correlator or by a gated double integrator of our own design.