When talking 600-700-900 series, it's really the depth you're looking at. A 600 series is always 60 cm in depth, a 700 series is always 70 cm in depth and a 900 series is always 90 cm in depth. When the depth is found, one then speaks as single, double or triple units of 30-40 cm width. It is easiest to understand if we are talking, for example, a frying plate, which will have 1, 2 or 3 zones and be correspondingly wide (eg 40-80-120 cm. Wide).
In addition, there are a number of "obsolete" devices that are not part of an actual series. It could be a sausage roaster, a table model of a roasting plate or similar.
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