Assertion: diver's depth | /r/HasProperty | up to 20 metres
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Source sentences:
text: This was developed further with the Modell 1915 "Bubikopf" helmet and the DM20 oxygen rebreather system for depths up to 20 metres (70 ft), and the DM40 mixed gas rebreather which used an oxygen cylinder and an air cylinder for the gas supply for depths to 40 metres (130 ft).