What do those camcorder sensor numbers mean?

I just bought a Sony HDRPJ260V. Manual says it has a 1/3.91 type, 4.2 mm sensor. 4.2 mm I hear means the diagonal of the image sensor. A Canon HF R300 camcorder has a 1/4.85 sensor. How can I tell what the diagonal is (isn't this the important thing, surface area of the sensor, one with 2X area should be 2X... show more I just bought a Sony HDRPJ260V. Manual says it has a 1/3.91 type, 4.2 mm sensor. 4.2 mm I hear means the diagonal of the image sensor. A Canon HF R300 camcorder has a 1/4.85 sensor. How can I tell what the diagonal is (isn't this the important thing, surface area of the sensor, one with 2X area should be 2X as good all other factors equal)? Should these numbers be proportional i.e. 4.2/(1/3.91)=X/(1/4.85)?

Seems like the manufacturers have conspired to purposely give you info that means nothing to you...or give you useful info but then conspire to not tell you how to interpret it. This reminds me of the megapixel hype nonsense in mini digital cameras but in reverse (manufacturers found higher MP ratings sold more cameras but more pixels in same size sensor does NOT necessarily mean a better image).
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