The Null function on the OP184 is used to trim the input offset voltage. It is
an optional function. If you are not going to use the offset nulling circuit
then leave these pins open circuit.
To implement the offset adjust use a 20K resistor between pins 1 and 5 with the
wiper to the negative terminal. The null range is +-1mV which is good for this
One thing to be aware of is that this is the Null at mid point. As you may
know, the rail to rail inputs have a trip point where the NPNs and PNPs switch
and the offset is the highest. So even if we null at 0 common mode, the offset
changes with common mode.