Why do some multimeters have discrete ranges for measurable values and some just measure based on signal type?
The ones that don't require you to set a range have a feature called "auto-ranging". It's a feature that makes the meter easier to use &mdash; especially in the field &mdash; but sometimes slower to settle on a reading. It adds a bit of complexity to the meter logic (and the user interface), which is why the cheapest meters don't have it.