Vernier Bevel Protractor

pls click on fig. to be clear
Simplest angle measuring instrument.It consisit of :
i. Main Body
ii. base plate stock
iii.Adjustable blade
iv.Circular plate containing vernier scale
v. acute angle attachment
Above fig shows the Vernier Bevel Protractor with acute angle attachment.The body is designed in such a way that its back is flat and there are no projection beyond its back.The flatness of the body is tested by checking the squareness of blade with respect to base plate (blade at 90 degree)
the base plate is attached to the main body, and an adjustable blade is attachedto a circular plate containing vernier scale. The adjustable blade is capable of rotating freely about the centre of the main scale engraved on the body of the instrument can be locked in any position.The base of the base plate is made flat so that it could be laid flat upon work.Blade can move through its length and reversed. It is 150 or 300mm long,13mm width and 2mm thick.
bevel protractor are tested for flatness,Squareness,parallelism,straightness,etc.