The Flic Film Precision Temperature Water Bath is custom built to fit four 500ml square bottles (included with the kit) and a Paterson Tank (not included with the kit). The tanks are guaranteed to hold the temperature to within 0.1 degree Celsius. The units are built with smart tech thermostats and variable voltage heaters so that there is no oscillation around the target temperature. Home color developing will be infinitely easier with these kits.