Drivers of fatigue-regulated heavy vehicles must record work and rest. The traditional instrument is the written work diary; an EWD is the approved electronic replacement, and only systems approved by the NHVR may be called one.
The value is accuracy and real-time visibility: an EWD can warn before a breach instead of documenting it afterwards. See fatigue management and the fatigue and work diaries guide.
General information, not tax or legal advice.