Do I need the MATH option (suffix code /M1) to install a pulse input module on the MW100 for calculations?

No. When installed, you can use pulse input module integration calculations. However, for any other calculations besides integration, you will need the MATH (/M1) option. Also, you will need the report function (suffix code /M3) if you want to make such things as integral flow reports (hourly, daily, weekly, monthly) or integral bar graphs of watt hours. Report data is saved in text format, therefore after data acquisition you can edit it in any template form using Excel or another program.