8.306624 to six decimal places. I think it's an irrational number like e or pi. Someone once showed be a graphical way of working out square roots but I'm buggered if I can remember it.

If you're interested.... https://sciencing.com/calculate-square-root-hand-5081134.html Me? My phone has a calculator app. Also, my math teachers always told me to do algebra using surds (fractions where one part or the other is a square or cube root) whenever possible. For example, sin(45) = sqrt(2).