For a slave recorder of lower sensitivity, R4 and
the resistors in the chain would have to be larger;
e.g. for a 10mv recorder R4 should be 5kQ and the
10Q resistors should be 100Q each.
Con8truction. The unit is conveniently assembled
in a steel 4in. x 4in. x 1iin. junction box. The
switch is an ordinary 11-position rotary type and
the 10 Q resistors are mounted on it; Iw 1%
tolerance 'high-stability' resistors are used for
these and for R3 and R4. A circular scale is provided
for the switch knob, marked 'OFF, 0, 0 1 .. . 0-9'.
Resistor R2 (which should be wire-wound) has no
knob; its short shaft has a slot for a screwdriver. It
is convenient to have the unit fixed to the stand
carrying the main instrument, and to connect the
recorder through a jack plug and socket, so that it
can be unplugged and used for other purposes when
not in use.