Well... it's simple. It in does what it is supposed to do. If you're being lazy with *nix reading, it's another utility that doesn't require shell knowledge.

The rough is this... you drag and drop an unmounted dmg file in a little square box that appears after you open it. A box pops up with the SHA-1 calculated checksum and a little radio button you can click on MD5 to show that checksum instead.

Then, you cut and paste the checksum that you found posted where you downloaded it from into the empty box. Press enter and it tell you either... it's not the right length... that is... you made a mistake cutting and pasting by one letter... it matches... or it doesn't match.

The whole process requires as little knowledge as could be possible for a person wanting to check a checksum manually.

(for those that don't know what a checksum is... or why it's important... i'll try to explain. Say you just spent the last 3 weeks making a program of yours oh-so-sweet. Now, you upload it to your website for others to be able to use it. A person with too much time on there hands thinks it'd be the funniest thing in the world to modify your oh-so-sweet program so that the pictures of the logos now have naked women or hentai with some voice. Well... since you aren't catering to that clientele you might find yourself in a difficult place, right? Hence... checksums are mathematical equations that prove.. 'if they match' that the program/item hasn't been tampered with. Someone out there is saying... why not just tamper with both the program and the displayed checksum. Well... besides other things... that involves a whole lot more work and effort which is fairly pointless since most people don't check the checksums anyway.)