With Gravity on, you can placed associated Level (Z-elevation) Dimensions on slabs, roofs, and meshes.

This guy.

(As with regular dimensions, the text can be customized, breaking the association. I use these on reflected ceiling plans, since you can't get gravity to detect the bottom of an element. A wish. (There might be a way to use a label for this, but I haven't tried.))

You should use associated Level Dimensions to show all the surface elevations in the project. Here's the slab stepping down in a theater:

You can also put grade elevations on a site mesh. Here I used the house outline as a guide to show the elevations at the corners. I don't know whether we should actually do this, but it sure is easy. (Also, there should be a way to display sea level, but I can't find it.)

UPDATE: To show sea level, assuming you have it set properly in Working Units and Levels: After placing the dim, select the text. In the Info Box, click the flyout at Measured Value and choose Autotext. click the flyout to the right in the same tile and choose "to sea level". I didn't bother updating the picture, so you'll have to take my word for it.

To place an associated Level Dimension, activate the tool and turn gravity on for the desired target, by clicking the slab, roof, or mesh gravity button. Then just click on what you want to dimension.

If the dimension value is wrong, it's because gravity detected the wrong element. For example, you're trying to get the main floor deck elevation and gravity is finding the ceiling. Hide the layer of the element that's in the way.

Tip: If you select the Level Dim and hold the mouse button down, you can see what element it's associated with. (This works for regular dimension ticks too.) This helps you track down elements in the way. Select the interloper, then use the Quick Layers palette to hide its layer.

There are different ways of doing this, but the first I've been pleased with is the use of Quicksilver.

With Quicksilver running, invoke it (Ctrl+Space, unless you changed it). Type enough of the word "ArchiCAD" to have it pop up on the left. If you have multiple versions, select the proper one from the list below.

Tab. Type "Lau". You should see "Launch Another Copy". Return.

There ya go.

If you don't see the "Launch Another Copy" option, quit Quicksilver, relaunch it, and try again. I have seen this happen after launching another copy, quitting it, and trying to launch again. Seems like a bug.

It isn't needed, but there are times when it's very convenient. You can quickly copy and paste from another project. You can open a placed module without closing the host project. It comes in handy.

Run multiple copies at your own risk. Keep your head on straight. Don't run two all the time. Don't open the same file in two copies at once. Quit the second one when you're done with it. Pay attention to where the second copy is on the dock. All these warnings go double for people who are easily confused, you know who you are.

Another tip: When quitting two ACs, let one quit all the way (the black triangle disappears from the dock) before quitting the other. If you quit them both simultaneously, you're asking for corrupted preferences.

Quicksilver is a "launcher", but it does much more than launch applications. It figures out everything about your computer, then hooks everything together so you can perform actions in an intuitive manner. It knows your files, your songs, your address book. You can find a file, say mail it, find the recipient, and done. No Finder, no dragging, no Open dialog.

I've had it for one day, so I'm no expert. Here's 3 links.

It's free. It's in beta, so you'll might hit a bug, although I haven't. It will also tell you to update every once in a while, which you should do.

It also offers a simple way to run multiple sessions of ArchiCAD.