My Nook HD+ Guide shows 3 types of SD cards are supported: Micro-SD, Micro-SDHC, & Micro-SDXC, The instructions include the following limits: 1) "micro-SDHC cards up to 32GB, Class 6", (no class 10 mentioned.); 2) "micro-SDXC cards up to 64 GB" (class is omitted); & 3) "The UHS speed for micro-SDXC cards is not supported". What is the difference between SDHC class 6, SDXC class 10, & SDXC UHC, What is UHS? Are these “old” guidelines”, are they now interchangeable, and if not, why? Is this a speed issue, a design issue, or is there a physical difference? Under these guidelines, will a micro-SDXC 64GB class 10 (that does not list or include any UHS reference), work? Is UHS-1 the same as Class 10 or something new and "physically" different? If the nook is limited to a 32GB class 6 SDHC card, but can also use a 64GB Class 10 SDXC card, where does this UHS definition fit? The nook info is recent. The limited explanations of SDHC; SDXC, and UHS terms leave me too confused to confidently choose the right SD card for this situation. I didn’t find Class 6 microSDXC cards, will a (faster) class 10' SDXC work, most of them also list UHS, what is the difference? To add the Android to a nook requires an SD card, I’d prefer to use the larger 64GB instead of 32GB. Your guidance would be appreciated. Thank You.