Cutting stepped tenons - step three setting the back fence

The back fence needs setting exactly to a tight sliding fit with the template fitting between the cut on the sacrificial piece , the template in the middle and flat piece of against the fence (I've used mdf. Just in case the fence isn't perfectly parallel to the cross slide make sure you take the settings from the same part of the fence.
This distance now set will give the longest side of the tenon accurately. Why I've used the MDF as a removable space will become apparent.