Let me first explain, why I reached there. I noticed that Canon G1X has a smaller sensor than normal APS-C but more pixel count than many 4/3 sensors, so maybe the pixel density is higher, so according to the law of physics that says bigger pixel size means better quality, it may end up a noisier sensor. Now back to the question, how we calculating it's 1.5" and why is Nikon CX is 1"? Lets take the example of CX format as its easier to see 1" as a whole number. The physical dimension of CX sensor is: 13.2 x 8.8 The diagonal length would be: 15.86 From Maths: Square root (Square of Height + Square of Width) Now 15.86mm is 0.62in as 25.4mm is 1" So if this the sensor diagonal length is not 1" then what is this 1" in Nikon 1? Similarly 4/3 means 1.33" while the diagonal length is 0.85" accordingly Similarly Canon G1X got 1.5" sensor and the diagonal length 0.92" According to the 4/3 standard definition, I found it is the diameter of the 4/3 tube, so is it the image circle? well in that case to get the 1.33" image circle, dont we need 1.33" diagonal length on the sensor? I know you guys are Photographers, but I also know you are the only people I got to ask such question, with huge photography experience and knowledge about history and mechanics of numerous camera systems and most importantly a passion to learn more and share/discuss the ideas. Thanks for reading!