We are in the Architectural Coatings industry (House paint and caulking). We need mobile App that will calculate the amount of Product required for a given Area. This App will be used by Contractors at the job site to estimate the cost of material for their clients. For example: User enters "1,000 square feet" as the Area and the the app will say "You need 10 gallons of Product X or 5 gallons of Product Y or 7.5 gallons of Product Z". Then the User may select the quantity of each product the desire and it shows total price. There are about 50 products involved. Currently this calculation is performed by an Excel spreadsheet so all values are already known. App must work without internet connection (offline), but it will be updated via the internet every 3 months.