The triangulator is essentially a wireless compass. It will point to the nearest transmitter on the frequency its on. The frequency change GUI is opened by right-clicking while sneaking. If there are no active transmitters in this dimension or you are using a remote at the same time the triangulator wont know where to point. For the techy guys the triangulator doesn't actually point to the nearest transmitter, rather it adds all transmitters on the frequency based on their distance to the player in the ration 1/d therefore if you have 3 transmitters 20 blocks east and 1 transmitter 10 blocks west it will point east. So if you want to confuse someone using a transmitter to mark their way home put 5 somewhere nearby.
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