Unplug the radial arm saw for safety, put on safety glasses.
Raise the saw to get access to the table. Brush off any sawdust or debris from the saw.
Check the saw for square. Lower the saw until the blade meets with the front table. Raise the blade one quarter turn. Place a framing square on the front edge of the front table and next to the blade. Pull the saw forward. The blade should not dig into the top or pull away during travel. Adjust as required by loosening the bolts from under the front table where it attaches to the steel base with a adjustable wrench. Retighten the bolts.
Check the table to be sure it is flat. Lower the blade until it contacts the front table. Raise the blade 1/2 turn. Pull the blade forward slowly, noting the gap between the table and the blade. The gap should be the same throughout its travel. Adjust the saw to 45 degrees left and right and check the gap again. It should maintain the same gap throughout the blade's travel. If it is not flat and true, you will need to shim the top from below as required until it is true.