Two marching compases by Singer and Barber, 1850-1918.
© Science Museum / Science & Society Picture Library
The two marching compases illustrated are both open to reveal the face of the compas. The compas above is a prismatic compas of 1918 made to Verner's pattern Mk VIII and adapted for night marching. The compas below is a Singer patent marching compas made by Isaac Merritt Singer (1811-1875).