It's doesn't have an accelerometer and he's using an external antenna so it wouldn't matter. You don't need to mount the vbox at all when using an external antenna.
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Keep in mind that the PBox has a frequency of 10 Hz and the VBox is 20Hz. It was the reason I ordered the vbox and gave up having the display of the PBox.
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One more thing to try. To make sure it thinks it's connected to the external antenna, run the iOS app looking at the satellite count and then place any metal plate over the vbox (not the external antenna) and you should see the satellite count unchanged. If you tried that without the antenna plugged in, the count would go to zero.