#fore-staff

[historysurvivalguide]

The description and use of the sector, crosse-staffe, and other instruments : with a canon of artificiall Sines and Tangents, and the use thereof in astronomie, navigation, dialling and fortification by Edmund Gunter (1636)

A simple device to measure angles in sky. By measuring the angle between the horizon and Polaris an observer can determine their latitude