The Hilger Watts TB5-2 Precision Box Level is a magificent piece of engineering- measuring 8" on each side. The bubble level is accurate to .0005" in 10 iches or 0.05mm per meter. There is a small subsidiary level under the main bubble to make sure the box level (or Block Level) is square in the perpendicular. Two of the level's faces are precision ground flat, while the other 2 sides have vee grooves machined in them for use on rods or shafts. These will come in their factory bakelite cases- beautifully made.