This Douglas Square Protractor is custom made by Hammond Aviation for training and navigational purposes. Your first quality 5″ x 5″ Douglas Protractor for your chart navigation needs! Constructed of durable Lexan®, this plotter won't melt, warp or break in extreme temperatures. Its convenient 5-1/8" square size and ease of use make this plotter a pilot favorite for simple, accurate flight planning. The 2 NM grid makes alignment with parallels simple.