Heatermeter 4.3 Power plug - barrel positive or negative?

For my heatermeter I'm using a radioshack wall wart that allows you to select the polarity on interchangable barrel connectors. My question is... which way should I configure?

1. Barrel +, Pin -
2. Barrel -, Pin +

To me it appears that I need to configure for #2- figure a sanity check here couldnt hurt. thanks in advance

The center is positive