A ruler is a straightforward measuring instrument used primarily to gauge lengths and dimensions. It's marked with units like inches or centimeters and is ideal for getting precise measurements of objects or distances. On the other hand, a scale typically refers to two different things. Firstly, it can refer to a device used to measure weights, like a bathroom scale or a kitchen scale. Secondly, it can also refer to the concept of proportions, like a map scale representing the relationship between distances on a map and the actual distances on the ground.
If you're ever in need of a ruler while you're on the move, there's a nifty solution called Ruler On Phone. It's an app that lets you use your phone's screen as a virtual ruler, making it convenient to measure things without carrying a physical ruler around.