How can I calculate volumetric speed for Slic3r auto speed?
Auto speed is calculated from maximum volumetric speed in mm3 per second. If you normally print at 80 mm/s, your extrusion width is 0.5 mm and you are printing 0.2mm high layers, your volumetric speed would be 80 * 0.5 * 0.2 = 8 mm3/s, which is the volume of plastic extruded by your printer every second when printing at that speed (not accounting for any die swell).