Using SeisMac

When SeisMac is started, it will try to access the laptop's Sudden Motion Sensor (SMS). If SeisMac cannot find an SMS, then you'll see this window:

This will happen if your laptop does not include a SMS. Unfortunately, this can also happen on certain G4 laptops that do include the SMS (for further details see the FAQ). Either way, you can choose to quit, or to run SeisMac with test data.

If your laptop is supported by SeisMac, then you'll see the main window:

The window displays a continuously scrolling record of the three axes of the Sudden Motion Sensor:

• The X axis measures accelerations towards the right (positive values) and left (negative values)
• The Y axis measures accelerations towards the rear (positive values) and front (negative values)
• The Z axis measures accelerations towards the top (positive values) and bottom (negative values).

The three graphs continually move left as new points get added on the right and the old ones disappear off the left. Once per second a blue vertical line appears on the right with a time label on the bottom.

With your laptop sitting quietly flat on a desk, the three graphs should be about centered (note that the Z axis is centered on 1G instead of 0G). However, it's much more fun when you stimulate things, though. For instance:

• Sit your laptop on a desk, and tap your foot on the floor underneath.
• Tip your laptop to one side, or to the rear.
• Tap the various sides of the laptop.
• Pick the laptop up and gently move it about (but see the disclaimer!).

Scroll bar and Real Time button

Earlier versions of SeisMac were locked into Real Time mode, with the graphs always moving left. Once a part of the graphs disappeared off the left side of the window it was gone forever. No longer! Drag the scrollbar on the bottom towards the left and you'll move back towards when you started SeisMac, viewing older seismic events.

Notice that when you let go of the scrollbar the graph stays in place rather than moving left. You've turned off Real Time mode, and the window will keep displaying the same region of the graph as long as you like. To turn Real Time mode back on, you can a) click the Real Time button to the right of the scroll bar, b) drag the scrollbar all the way to the right, or c) press the space bar.

Once the buffer is full, the earliest data in the buffer will start being discarded, so that the buffer always contains the most recent X hours of data (where X is the buffer size chosen in the Preferences window). As a special case, if you're viewing a fixed area of the graph then you will be able to view it forever, even when the data being shown has been discarded. However, if you then touch the scrollbar you'll be forced back into the live area of the buffer and the area you were looking at will be lost.

Expand and Contract buttons

At the bottom right of the window are buttons to adjust the horizontal and vertical scale of the graph:

		Expand horizontal: stretch the graph in the time dimension
		Compress horizontal: shrink the graph out in the time dimension
		Expand vertical: stretch the graph in the acceleration dimension
		Compress vertical: shrink the graph in the acceleration dimension

Out of Range arrows

When the acceleration is too high or low to fit in the graph, an Out of Range arrow will appear to show you which direction the graph has gone.