English: Drawing of Riefler escapement, invented by Sigmund Riefler in 1889, from the catalog of the Columbian Exposition, Chicago, 1893. It was used in the precision astronomical regulator clocks produced by the German firm Clemens Riefler from 1890 to 1965. The escapement's advantage was that it applied impulses to keep the pendulum swinging by flexing the suspension spring (i) that supported the pendulum, rather than applying force directly to the pendulum. The spring is attached to a metal support (A) that rocks back and forth on knife edges (c) resting on agate plates (P). Riefler clocks achieved an accuracy of 10 milliseconds per day, possibly the most accurate all-mechanical clocks ever made. Alterations to image: rotated image 90° CW, rotated R drawing a few degrees to justify, moved R drawing closer to L and aligned drawings vertically, converted to 32 color PNG.