The coloured segments each span 3 minutes and show the period during which radio silence is observed to listen for distress calls on the international distress frequencies.
By: kjkt3 : May 11th, 2020-16:03
The red segments indicate the listening periods for distress calls made with CW (morse code) and the green segments indicate listening periods for voice calls, usually on frequency 2182 kHz although other frequencies are also used.
I believe that Eddie Platts, who owns TZ-UK, also owns the Smiths brand and produces (well-made & appropriate) Smiths watches. Eddie's a 'good guy'. [nt]