Dwell meter question

[corvette8n]

Found a dwell meter from early '70's on my garage wall, it has only two connections on it red & black(I assume + and - ). My question is where do I hook this up to test with? My car is a '41 v8 with a remote coil kit, can style coil is mounted on fender. Only instruction on meter is to double the reading when testing a four cylinder. What kind of reading should I get on the dial?