The following is an example of a custom license metric script.

Note: This example is for demo purposes only and is not meant to be used for actual compliance scenarios.
<script><![CDATA[getRightsForDevice();
function getRightsForDevice(){
var rightsForDevice = -1;
	var deviceRecord = new GlideRecord('cmdb_ci_computer');
	if(deviceRecord.get(entity)){
		rightsForDevice = deviceRecord.getValue('disk_space');
	}
	return rightsForDevice;
}]]></script>