The biggest division in SD card seems to be between dealing with SD and SDHC. I’ve been testing with a 128MB, 2GB and 8GB card and the 128MB one gives the best results so far. I think this is mostly because of timing – a smaller card means there’s less to keep track of in the filesystem, which makes the filesystem operations faster, which makes the timing bugs surface less frequently. I think I can get over these bugs though, so anything <=8GB should work. Henrik: You're absolutely right, there should be plenty of time to switch between inputs and sample them all. But there's some feature creep there and the implementation details get a little hairy... the meter firmware doesn't store settings for the channel not in use, the app doesn't have a clean way of inputting them, etc. Sampling all the channels in the log is doable, but for the first release of the logging feature it will be 2 channels.