How to use a light meter Pt. 2
There are two types of light meter reading - reflective and incident. Your camera has a reflective light meter which measures light reflected by the subject.
A hand held light meter measures the light falling onto it and it's called an incident light meter reading.
Hand held light meters are much more accurate than you camera's built in meter because the reflective element is removed. You are measuring the available light that's actually falling onto your subject.
The incident meter converts the amount of light measured into exposure settings which you transfer onto your camera using manual exposure. You can scroll through shutter speed and aperture combinations to find the depth of field you want to use.
When you use an incident meter you must remember to set the ISO on both meter and camera as the same. If you don't the the reading will be wrong because one is set to a different light sensitivity to the other.
Of course the problem with hand held meter reading is when you're photographing something that's a long way off and in different light to where you are such as a mountain range which might be in sunshine, whilst you're standing in the shadow of a cloud.