Is the LM399 Temperature coefficient with the heater on or off?

The LM399 datasheet specifies a temperature coefficient "$$\\Delta\$$T/$$\\Delta\$$Temp". The conditions state an ambient range but don't specify if that's with or without the heater on.

Which is it?

• Where the Temperature Coefficient goes, I see dV/dT, but no dT/dT. Whatever it is, T is the temperature that the Zener sees, doesn't matter with or without the heat from internal or external heater. BTW, could you answer, please, this one, if you know it?
– jay
Nov 25, 2021 at 23:10