an overall negative impact on the business with each unit being shipped at a loss once product and distribution costs including payments to wireless carriers were factored in. Amazon has never published sales figures for the device though stated in a Press Conference that they had shipped more Kindle 3 units than the final book in the Harry Potter series. Additionally, operators are beginning to sell advertisement-supported Kindles with 3 G connectivity at the same price as WiFi-only models. 15 Given that this is a business with a market capitalisation of $90 billion it can be safely said that some short-term pressure on margins will probably turn out to be a good longer-term investment and this may well be an example of short-term investor sentiment conflicting with a sensible longer-term strategic plan. Only time will tell. Time will also tell if other bistable display options prove to be technically and commer- cially viable. Qualcomm, the company that provides the EVDO and now 3 G connectivity to the Kindle have invested in a MEMS-based bistable display described technically as an interferometric modulator and known commercially by the brand name Mirasol. The display consists of two conductive plates one of which is a thin-film stack on a glass substrate, the other a reflective membrane suspended over the substrate. There is an air gap between the two. It is in effect an optically resonant cavity. When no voltage is applied, the plates are separated and light hitting the substrate is reflected. When a small voltage is applied, the plates are pulled together by electrostatic attraction and the light is absorbed, turning the element black. When ambient light hits the structure, it is reflected both off the top of the thin- film stack and off the reflective membrane. Depending on the height of the optical cavity, light of certain wavelengths reflecting off the membrane will be slightly out of phase with the light reflecting off the thin-film structure. Based on the phase difference, some wavelengths will 15 AT a