Better way to adjust speedo?

[mustang70]

I noticed today my speedo is off about 5mph. The drive ratio was set to 3.27 so I changed it to 3.55. I also adjusted tire size to closer to the actual size. The speedo was still off. The reluctor wheel was set to 13.70 teeth. From what I found the T-56 has 12 teeth. Is it better to adjust that or PPM?

 

[mustang70]

Nevermind. I think figured it out it's the PPM. Now I just need to figured out which way to adjust them.