Protractor on the dial from 180°, as the dial is graduated from opposite zero marks to 90° each way. Since the spaces, both on the main scale and the Vernier scale, are numbered both to the right and to the left from zero, any angle can be measured. The readings can be taken either to the right or to the left, according to the direction in which the zero on the main scale is moved. Reading the Vernier scale: The bevel protractor Vernier scale may have graduations of 5′ (minutes) or 1/12°. Each space on the Vernier scale is 5′ less
Vibrations of a circular membrane equation with zero boundary conditions, Due to the circular geometry of formula_1, it will be convenient to use cylindrical coordinates, formula_13 Then, the above equations are written as Here, formula_16 is a positive constant, which gives the speed at which transverse vibration waves propagate in the membrane. In terms of the physical parameters, the wave speed, c, is given by where formula_18, is the radial membrane resultant at the membrane boundary (formula_19), formula_20, is the membrane thickness, and formula_21 is the membrane density. If the membrane has uniform tension, the uniform tension force at a given radius, formula_22 may be