Variation of the derived detector orientation with the hour angle at time of observation. Coloured points show individual measurements for four globular clusters, with clusters being offset by 0.04^° for clarity. The solid sinusoidal lines show the predicted variation due to a polar axis offset of 0.017^°. The change in detector orientation due to this effect increases towards the poles, with NGC 104 (δ = −72^°) showing the highest amplitude.