Here is what I did using the street, an rpm gauge and an rpm calculator....
First make sure the odometer is right on the mile and get an odometer gear adapter that goes on the outside of the xmission speedo cable outlet, if necessary.
Then rotate the arm inside the speedo gauge where the needle coil-spring attaches until the speed matches a given rpm.
Use a rpm calculator online.
This can be tricky and take several tries as the very slightest rotation has quiet an effect on the reading.
I set the sweetspot to be accurate around 40-70 mph, as the speedo needle is not 100% across it's entire range.
If you don't want to putz around, just bring it to a speedo adjustment shop.
