Triple modular redundancy

[5] Called repetition code, some communication systems use N-modular redundancy as a simple form of forward error correction.

The general case of TMR is called N-modular redundancy, in which any positive number of replications of the same action is used.

The number is typically taken to be at least three, so that error correction by majority vote can take place; it is also usually taken to be odd, so that no ties may happen.

Thus, the majority gate output is guaranteed to be correct as long as no more than one of the three identical logic circuits has failed.

[6] TMR systems should use data scrubbing – rewrite flip-flops periodically – in order to avoid accumulation of errors.

[14] However, such a large number was usually only carried on ships undertaking survey work as was the case with the Beagle.

In the modern era, ships at sea use GNSS navigation receivers (with GPS, GLONASS & WAAS etc.