On Thursday, July 4, 2019 at 4:16:39 PM UTC-7, John Larkin wrote: ood for testing crystals.
Positive input to terminal 1, negative input to terminal 2, and the output is a current source proportional to the voltage difference; wire that to terminal 1. Either midpoint/ground terminal 2, or (if you want to get fancy and have more compliance range) use the second section amplifier with inverted input polarities and wire its output to terminal 2.
inputs won't like +/-9V range, but maybe you can power it with a couple of lithium cells and get by. One or two resistors, to bias the amplifier(s) is the rest of the part count. One chip, two resistors, two batteries. An Altoids box and some black paint and voila!