I am trying to determine the full amount of amps that a service is pulling. It is 120/240 single phase service.

I would use and Amprobe to determine that, If you can safely work with Electricity, Just clamp around each hot wire, set Amprobe to Maximum Current Expected(200)? It will show current of each circuit if 1 is Breaker is on at a time. It can be done with math.
Amprobe is much quicker, Have to be less than 50 bucks, Very basic tool.
Good Luck

Here's 2 models and prices:

Amprobe® Test Tools
That one measures to 400 Amps, and 4,000 Volts, also does resistance, capacitance and frequency(a little). Nice.

USED ~ AMPROBE ULTRA ~ - eBay (item 330265094393 end time Aug-29-08 17:25:06 PDT)