WTB - tach - not one to fit in dash

[incoma]

I just need a cheap tach that I can use to monitor my rpm while I'm driving. Nothing expensive. Actually, if I could borrow one in the OKC area for 1 week, that's all I need. I just want to see how my rpms change in the different gears, od/drive, and highway. I want to be sure my math was accurate when I ran the numbers.

I drove the truck today for 40 miles, and got up to 75mph. First time the truck moved that fast on its own power for 7 years. I even turned on the A/C!! What a wonderful feeling.