Most folks will make a small mark on the leading edges of each rudder about an inch below the transom. Make a matching mark on the trailing edges at the same height. Measure the distance between the leading edge marks and the trailing edge marks. If they are the same, your rudders are square. If the leading edges are closer together than the trailing edges, you have toe-in. Most folks further confirm this by making additional marks on the leading and trailing edges of the rudders very near the bottom and repeating the measurement. Classes sometimes have slightly different tuning recommendations on rudder alignment.