Work with ratios two ways. In simplify mode, enter a ratio like 40 to 16 and the calculator reduces it to its lowest whole-number terms using the greatest common divisor, so 40:16 becomes 5:2. In proportion mode, enter three parts of an equation A:B = C:D and leave one blank, and it solves for the missing value, which is exactly what you need for scaling recipes, mixing ratios, resizing images or reading maps. Keeping ratios in their simplest form makes them far easier to compare and reason about. Both modes handle decimals and update the moment you change an input. Everything is worked out locally in your browser, with no data leaving your device at any point.