KPI

Material usage variance would be fine, though investigations are needed to determine the cause eg poor material or poor utilisation of it.

Idle time measures the cost of the workforce being paid whilst doing nothing….so they are wasting their time, though this might be outside their control eg if a machine breaks down. However, I think that labour efficiency variance is needed to complete the picture. This is caused when people work but are still wasting time by not producing enough. Causes have to be determined.