We describe a simple technique for creating etch pits in muscovite mica substrates for calibration purposes in atomic force microscopy (AFM). The etch pits are produced by wet etching the mica substrates in concentrated hydrofluoric acid and are formed with specific geometry. Along the long axis of the etch pits, steps of approximately 2 nm are observed which correspond to the molecular planes of mica. These steps bifurcate into 1 nm steps along the short axis. It is these 1- and 2-nm-high steps that permit height calibration.