This is an absolutely essential tool for anyone with a DC system in a boat. Not all clamp meters are the same. The REALLY useful feature is the ability to measure DC currents down to very small values. This one is the only one I know of that will do it, without spending a bunch of money. Yeah, not cheap compared to many clamp meters, but read the specs: most clamp meters will not measure small currents, and certainly not small DC currents. These meters are all made by Extech as far as I know, though sold under a couple of different brands.

Once you get used to using this you will not understand how life was possible before. You can clamp it on any wire and measure DC currents down to 10 mA. This has enormous potential for debugging. Finding where leakage is, understanding what device is consuming all your amp hours, etc. It also measures currents as high as 200 amps, so good for debugging charging systems too. It doubles as a normal DVM, and though I find it less convenient to use than a Fluke (which I also carry) if it is all you had space or money for, this would be what I would have.

You can use it in peculiar ways. For example, I have had fuses blow that are feeding several devices (I know, you shouldn't do that). By setting the DC amp function on Max-Hold and clamping it on the various feed wires, the instantaneous current necessary to blow the fuse will register on the meter, identifying the culprit.

On a boat, you will reach for this nearly as often as you reach for a normal voltmeter. Like the Tillertard, I have a 1 Ghz digital sampling oscilloscope with a 100 KHz bandwidth DC clamp probe - but this little clamp meter is more useful by far on a boat.