This course indicator comprises a flexible rule (scaled in inches) pivoted in two 360-degree compass cards. The bottom card carries a magnetic variation scale and a compass error check scale, all in black. The top card has a red deviation scale and two setting arrows, all in red. The Sestrel-Luard was designed by Commander W.B. Luard, RN, as a replacement for the parallel rule for use with charts. The instrument allows one to plot true, magnetic or compass courses or bearings.