Thank you for this how-to guide, even a lay person like me has been able to make a heater band for my DSLR. I had to make one that is powered off a portable battery pack with a 5V USB port, so the spreadsheet was incredibly helpful for working out the required resistance and length. Just tested the device and it seems to work perfectly. Will do a proper field test as soon as the sky is clear. Hopefully this will enable me to capture star trails for more than 1-2 hours at a time. Thank you again for this wonderful resource, you are great!