Which are the primary instruments in my PA28-200R?

[Morgan3820]

So I am filling out the form for the EI CGR-30p. RPM, CHT, EGT are standard. I am allowed five more primary functions. MP obviously, as is oil pressure, temperature, fuel pressure. That leaves one primary function left. The amp meter is on the panel in the cluster beside the CHT, but is it primary? Fuel flow is with the MP gauge. So do I take Fuel flow as my remaining primary? I want to get this right the first time.

 

[Forkauto]

 

[EchoDelta]

 

[Jesse Saint]

 

[Reece]

 

[Jesse Saint]