Leica M-P Instructions Manual page 183

Superimposed image method (double image)
In a portrait, for example, aim the metering field at the eye and turn
the distance setting ring on the lens until the contours in the
metering field are brought into line. Then choose the subject detail.
Out of focus In focus
Split image method
When taking photographs of architecture, for example, aim the
range finder metering field at the vertical edge or another clearly
defined vertical line and turn the distance setting ring on the lens
until the contours of the edge or line can be seen at the limits of
the metering field with no misalignment. Then choose the subject
detail.
Out of focus In focus
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