by clinometers, e.g. for determining dip or strike of geological strata

Full Title

Compasses; Devices for ascertaining true or magnetic north for navigation or surveying purposes (using gyroscopic effect G01C19/00) > Magnetic compasses > with north-seeking magnetic elements, e.g. needles > Comparing observed direction with north indication > by clinometers, e.g. for determining dip or strike of geological strata