Type XXI class clocks

[Niume]

Hello why type XXI has these weird clocks with these red lines. What do they mean?
http://www.part.lt/img/a5c7f943e39324199a1592dfbd5270d410.jpg (http://www.part.lt/perziura/a5c7f943e39324199a1592dfbd5270d410.jpg)

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Labas vakaras!
As I've understood, they indicate three minutes of radio silence.
So it's for the radio room to listen for distress calls or something like that.

http://www.timefactors.com/smithsprs28.htm
http://www.germaniainternational.com/navy7.html

[Niume]

Ačiū! :Kaleun_Salute:

[Mussalo]

It reads "Bundeswehr" on the clock face so clearly a retrofit.
I wonder what kind of clocks they did have originally as in did they respect those listening times?