Gruen precision watches feature automatic winding and functions, including hours, minutes, seconds and the date. All Gruen watches have an improved safety pinion, patented by Dietrich Gruen in 1874. Military watches produced by Gruen during World War I feature corrosion-resistant cases, luminous dial markings and hands to fit within U.S. military regulations. Gruen also produced doctor’s watches with a separate second hand dial.
In the early 1900s, Gruen began designing watch movements to fit into fashionable rectangular and curved wristwatches. Rectangular Gruen watches replace small, round movements with larger rectangular movements that fill the available space in the watches. Watches featuring rectangular movements are sleeker because the cases do not need to disguise a round movement. Gruen Curvex watches feature a curved movement to fit the curved designs of the watches. The Gruen Curvex movements allow for thinner and more curved watches compared to competitors' watches with flat movements.
Following the success of the Curvex watches, Gruen designed a thinner watch movement and launched a series of watches called VeriThin. The VeriThin movement was designed to fit inside smaller watch case shapes. In the 1940s, Gruen released a line of wristwatches featuring the first VeriThin movements to be made entirely in the United States.