Lie board.It's low tech but black electrical tape on the bottom of the club, using a lie board will tell you if the angle is too flat too upright or just right every time. It's foolproof.

The best thing I have found is the Lie Board. If there is anything better let me know please.

I've always done it on a lie board and a piece of impact tape on the face

Don’t get too fixated on lie angle of your irons. If your well struck shots are going straight your lie angle is fine. If you are consistently pulling or pushing shots your lie angle may be off.

Not enough space to go into it here but if you do a Google search you will find a lot of disagreement regarding lie boards, tape, powder, etc. to determine your correct lie.

If you really want a definitive answer for yourself get it from a pro at a fitting, preferably with a launch monitor.