I need help. In this video Differential Amplifiers at 0:47:41, the transconductance Gm = ∂ΔId/∂ΔVin

I don't understand why both partial derivative ∂ and delta Δ used here.
I usually see that only one of them is used in the definition of Gm.
Gm = ∂Id/∂Vin or Gm = ΔId/ΔVin

 

I'm not going to even try to get 47 minutes into a video with my satellite connection, so I'm having to guess.

They probably have a function that uses the Δ simply as part of the name and then they are taking the partial derivative of one such function with respect to another.

But without see how the functions are defined, I can't tell.

 

Being a differential amplifier perhaps the Delta term refers to the differential voltage & current....??

 

Being a differential amplifier perhaps the Delta term refers to the differential voltage & current....??

Ah, I think you are right! I didn't notice about this.