Trying to run mathematical formulas while out on the job is difficult. This handy app makes it easy. The five most commonly used formulas are at your finger tips:
Where to set a stove in a corner Installation
What size hole to cut in the roof based on the roof pitch
How tall should the venting system be t meet the 3' 2' 10' rule
How far down does the chimney need to extend to meet the connector pipe clearances to a cathedral ceiling
Minimum room size required for proper combustion air supply in gas installations using the KAIR formula.