In most cases, when
measuring DC voltages in
an electronic circuit,
the black negative lead
is clipped to the
negative connection of
the battery or supply.
This leaves one hand
free.
The red lead is then
used to measure the
various voltages in the
circuit.
These voltages are
therefore measured WITH
RESPECT TO negative.
wrt = with respect to
In the diagram, point A
is 18 volts positive wrt
to D. (this is actually
the battery voltage).
Therefore D is 18 volts
negative wrt A.
A is +12 wrt C and +6
wrt B.
D is - 6 wrt C and -12
wrt B.
B is +6 wrt C and +12
wrt D.
C is - 6 wrt B and -12
wrt A.
Looking at the diode.
The anode is less
negative than the
cathode.
Or in other words, it is
more positive.
The anode is positive
wrt cathode by 1 volt.
