Produce Stickers That Test For Ripeness

so few answers provided by the article. Is there a release rate of ethylene that consititues a standard for ripeness (in ppm or some other measureable rate?), and if so, is it the same for all fruits and vegetables or does it vary depending upon the item? It seems to me that a cantelope and a tomato would probably have different quanitites of release simply due to their sizes. Does the thickness of the skin, membrane or shell surrounding the item change how ethylene is released? Will different stickers be required for each style of produce?

Maybe the growers could benefit from this, but time was, you could go to a fruit 'n' veg stall and touch and smell the produce - with a little experience, any average shopper could work out when stuff was ready to eat. W'appen?