Description
In the 17th to 19th Centuries, portable pocket sundials were used to tell local time by aligning them with the sun. An adjustable gnomon cast a shadow on a time dial, and a built-in compass was used to ensure it was oriented correctly for latitude and the time of year. They were used to tell local solar time which could be converted to mean solar time (clock time), with an equation of time scale. Though not as reliable as mechanical clocks, they offered independent timekeeping for travelers away from indoor clocks. They also offered an alternative to pocket watches which in this period were expensive and of limited accuracy until innovations of the 19th Century. Many pocket sundials were made of brass, sometimes silver or nickel plated, and sometimes with an additional hardshell case. Others were inset in wooden cases. The craftsmanship and accuracy of a pocket sundial manufactured in this period made it both a functional tool and a symbol of status and intellect.
Reference:
Compassipedia, Sundial Compasses, https://compassmuseum.com/sundials/sundials.htm
