Traditional Culture Encyclopedia - Hotel accommodation - What does the Japanese welding symbol BW3 mean?

What does the Japanese welding symbol BW3 mean?

This should not be a welding symbol. In the field of welding, BW2 and BW3 are used, some of which are product models, such as:

BW 1, BW2 and BW3 gas water heaters are water heaters.

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