Below is a very simple circuit to extract the transconductance value of the MOSFET.

As it is known, transconductance is known as Delta (Id) / Delta (Vgate).

For the gate voltage, I defined it as .step param X 0 12 0.5.

What I want to do, for example, is the amount of change from 0V to 0.5V, 0.5V - 0V = 0.5V or 1V - 0.5 up to 12 V. I want to do the same for Id corresponding to the amount of change and find their ratio.

Should I continue for every value like below:
.meas TRAN Vg FIND V(out) WHEN V(X)=0.5
.meas TRAN Vg FIND V(out) WHEN V(X)=1
.meas TRAN Vg FIND V(out) WHEN V(X)=1.5 . . .

doing the same for Id and using .meas DELTA param makes the process too long.

Maybe I am wrong but is there any other correct way to do it?