Which measuring tool is best for measuring the width of a milled slot?

The best tool for measuring the width of a milled slot is the dial caliper. This instrument provides precise measurements with a high degree of accuracy and is specifically designed to measure various features, including the width of slots, internal and external dimensions, and depths. The dial caliper has a clear, easy-to-read scale that allows users to take quick and accurate measurements, making it ideal for situations where precision is essential, such as in milling applications.

In contrast, a depth micrometer is primarily used for measuring depth rather than width, which means it wouldn't be suitable for this specific task. A laser scanner, while capable of capturing complex geometries with high precision, can be more cumbersome and may not be necessary for simple measurements like the width of a slot. A steel rule, while useful for basic measurements, does not provide the same level of precision as a dial caliper and may be more prone to human error in measurement. Therefore, the dial caliper is the most appropriate tool for accurately measuring the width of a milled slot.