Reporting a wrong result
If a tool gives an answer that doesn't match your own working, please include the exact inputs you used and the figure you expected. Every calculator on this site uses fixed geometry or clearly stated standard conventions, so discrepancies are either a genuine bug worth fixing fast or a difference in assumptions worth explaining on the page. Either way it makes the site better.
Suggesting a new tool
The best suggestions are jobs with one correct quantity: something you've found yourself working out on paper, or hunting through a merchant's website trying to convert their coverage figures. If it can be calculated from a shape and a defined conversion factor, it can probably become a page here.
What not to expect
DIYCalcs can't give structural advice, confirm whether a specific job meets Building Regulations, or recommend tradespeople or products. The tools show the maths; decisions about your project stay yours.