 Second, tension settings are calibrated to the exact specifications of the stone that they hold, therefore they can not be manufactured until the customer has selected a gem.Unlike other settings, which can be manufactured ahead of time regardless of the stone they ultimately hold, each tension setting is designed for a specific stone.The tension setting is calibrated by a computer, using light to identify the exact places the mount must apply pressure on the gemstone to avoid fracturing it through uneven pressure distribution.