The Meld Calc plugin enables users to evaluate mathematical expressions directly within their Obsidian notes using the fcal library. It supports basic arithmetic, percentages, and advanced calculations with precision. Users can write expressions, select them, and evaluate them via the command palette to either insert the result into the note or copy it to the clipboard. The plugin also supports variables and multiline expressions, making it ideal for handling more complex calculations. It includes built-in units, functions, and constants to enhance its flexibility for a variety of use cases.