This is a most versatile instrument used in non-precision measurements. It is generally used with surface plate for layout work and inspection. It consists of a rigid base whose bottom surface is made perfectly flat. A spindle carrying a scriber in a universal clamp is attached to the base. The spindle can be inclined to the base in any position and clamped in place by tightening the spindle nut. After tightening it, slight inclination can be further given for finer adjustments by an adjusting screw. Actually the turning of the adjusting screw moves the whole spindle assembly up or down thereby tilting it very slightly. The scriber can by slid up or down the spindle and at the same time tipped back or forth in any position. The scriber can thus be set at any position desired. The base of the universal surface gauge is generally grooved so that it may be used on cylindrical surfaces also. Two pins are also placed in the base to serve as guides when scribing from the edge of the surface plate
To set a universal surface gauge to a particular dimension, use can be made of a steel rule positioned at 90 degree to the datum with the help of angle plate and then lines can be scribed on the workpiece.
Many a time surface gauge is very successfully used for centring the work at lathe. It is capable of precision measurements also when used in conjunction with dial indicator.
