LVariable: RPM_needle

Hello,
I'm trying to create an SD profile.
Now I'm at the L variable "RPM_needle". The values there do not correspond to the rotational speed.
Before I do the math and calculate how to derive the speed: Do any of you know the corresponding formula?
Many thanks!

@fsh1hh That variable is coded to control the needle animation so you'd be better off using the 'A:PROP RPM:1, rpm' variable if possible? If not, here's the conversion (prop RPM on the left, L variable value on the right):
300.0, 0.0
500.0, 14.0
1000.0, 45.0
1500.0, 76.0
2000.0, 108.0
2500.0, 140.0
2700.0, 153.0
3000.0, 171.0
3500.0, 200.0 
@martyn
Hello Martyn,
thank you for the fast feedback. Then I actually prefer to use the A variable. And that's the way I go with "SUCTION PRESSURE, psi". (Whereby the displayed values do not match the display in the cockpit. But I hope to find a solution for that)