Yes it needs an uninterrupted live. I told the chap this and asked where he is getting the 12v from his reply was the ecu.

On my sierra i had a switch that would supply 12v and then various fuses and wired to whatever, im my mpreza that i used it on i used a multimeter to find a live on the back of the cluster that didnt drop on cranking.

He is saying tho that it doesnt even sweep to callibrate the zero, which is odd.