This has an audio taper track which is frequently referred to as A10K or 10K logarithmic. This is required because the human ear responds to loudness in a non-linear way. A linear track pot could be used, but in this circuit that type would seem to have most of the volume control effect near the anticlockwise end of the movement. In the kit this is supplied with the splined section removed so that it fits the supplied knobs correctly.