You can participate in the manometer (a type of draft gauge) loan program found in this thread:Manometer Loaner Program
As WNY said you need to measure your draft to be able to set up the new baro and to verify proper draft throughout the burn range.
If you want to buy a manometer they are available for a decent price on ebay, here is an example:
This link is broken, either the page no longer exists or there is some other issue like a typo.
If you can find a Dwyer Mark II model 25 for less than $35 including shipping that is a decent price.