Hobbies and outdoors
Darkroom print exposure after a size change, camping stove fuel left and needed, and Morse code timing from words per minute.
Fuel Canister Calculator
How much gas is left in a part-used backpacking stove canister, and how much fuel and how many canisters to bring for a trip.
Enlarger Exposure Calculator
The new darkroom exposure time after raising or lowering the enlarger for a bigger or smaller print, or after a change in stops.
Morse Code Timing Calculator
Dit, dah and gap lengths in milliseconds for any Morse code speed, the speed from a dit length, and Farnsworth spacing for learning.
Hobbies run on rules of proportion that are easy to state and easy to fumble in the moment. A darkroom print made bigger needs more exposure by the square of the change in distance, not in proportion to it. A gas canister's fuel is its weight less the empty shell, which the label gives, and a trip's fuel is people times days times boils. Morse code timing is fixed by the ratio of dots, dashes and gaps, so a sending speed in words per minute sets the length of every element. The pages here do that arithmetic exactly from what you enter and say where the real world departs from it: paper and chemistry still call for a test strip, and cold weather and wind change what a stove burns.