Gold colloids of known size provide a reliable means of characterising tip geometry and calibrating the Z-axis to piezoelectric response. The incompressible, monodispersive and spherical nature of the colloids can also be used to characterise the vertical dimension of co-adsorbed biomolecules. The standard kit has colloids of 5, 15 and 30 nm diameter, eight numbered mica-coated 15mm discs, a disc carrier and a magnetic pick-up tool. The extended kit contains additional colloids of 10 and 20 nm diameter.