Review on Digital Protractor Goniometer Professional Accuracy by Jeremiah Vishwasrao

It works almost as advertised and is easy to use. It seems accurate within my reference angles. Much of the critical information is provided by carefully reading the instructions. Be sure to record the duration of the key press. From power on to full power off 8 seconds. A short press turns off only the display. It takes 5 seconds to zero. Short converts absolute/relative measure. I removed a star because the instructions provided are in near-microscopic writing, which is a bit difficult for my 75 year old eyes, and some of the instructions require more elaboration. My first puzzle was the polarity of the battery. I finally saw the + engraved on the lid and hoped it meant + at the top. It was right. Most illustrations are clear and helpful. Some speak of a deviation of 0.05 degrees, but the corresponding representation does not help. I'm not sure what to do with them. I understand the difference between an absolute zero reference and a non-zero relative measure, but I'm not clear on how to set the reference angle against which relative measurements are made. Trial and error will likely settle things.