EE HAD MOUNTED THE GRADER WHICH WAS PARKED IN THE WEST SHOP BAY. HE THEN STEPPED ONTO THE FRONT TIRE OF THE REAR TANDEM TO MOUNT A CB ANTENNA ONTO THE CAB. AS HE DID HE LOST HIS BALANCE AND JU MPED FROM THE 5' TALL TIRE TO THE SHOP FLOOR LANDING ON HIS FEET. PAIN WAS FELT IN THE LEFT FOOT. HE WAS TAKEN TO GIBSON GENERAL E.R. EXAMINED, X-RAYED, DIAGNOSED WITH FRACTURED CALCANEOUS BO