There two types of voltage measurements typically taken by a
technician. These are the voltage across a component and the
voltage measured with respect to a reference point, most often ground.
Across A Component
The voltage across a component is measured by placing one probe on each
lead of the component. Two measurements are shown below.
To measure across a different component, both leads must be moved.
voltage across R10
voltage across R11
With Respect To A Reference Point
When measuring the voltage at a point with respect to a reference the
common (black) lead of the meter always stays at the reference point,
while the red lead is moved to the various points to be
measured. Two measurements are shown below.
from the top of R11 to ground
from the top of R12 to ground