[sdiy] Power supply and FETS

[RichR]

Hi all
A few questions for my first post.
I've built a few modules that require a +12v -9v power supply however the
rest of my modules run at +12v -12v as does my power supply.I've tried using
a resistor to drop the -12v to -9v but it reads as +9v when I do this.Is it
a case of using different value resistors from the -9v rail?If so how do you
calculate the correct values to use?Is there something I'm missing?

How do you measure the Vp of a J fet?

Thanks
Rich