Why the +/- 5 V Power Supply?
The +/- 5 Volts is the power supply requirements of the MAX 275
that we use.
We considering making the output supply swing +/- 10 V, but that would
raise the cost per unit to have
+/- 5 V and +/- 10 V power supplies. There were some other limitations.
We did consider these before choosing to keep everything simpler with
a +/- 5 V power supply.