I've just about got my fuel system finished and am ready to install an in-line fuel pressure gauge.

Does it matter if it's in a vertical or horizontal position?

I'm thinking no but just want to be sure...

Not on mine, it's loose on a hose and reads the same. I would place it so it is easy to read.

Nope. It doesn't make a difference.

If it's not at a 47.632 degree angle from vertical, it may not work correctly. I thought everybody knew that!

The Cap'n