MOTM

> According to the Musical Engineer's Handbook (Bernie Hutchins, 1975), 3a 
> (10), "The purpose of the resistor is to compensate for the offset due to 
> the current that actually flows into the other input."  It is important to 
> use in precision DC summing circuits.

This is sort of a "hand waving" answer you write on a test when you forgot 
the real answer :)


> The MEH also tells  how to calculate the value.

Well that part is correct.

>  I've wondered how important this resistor  is in an inverting summer.

Application dependent.

 I don't know the answers to question #2.
>

It's a toughie :)

Paul S.