'D', 'G' and S' of the DGS Scale stands for 'Distance', 'Gain' and ‘Size'. Size refers to the diameter of a disc shaped reflector, which would produce the same indication on the CRT, as that of an actual discontinuity of unknown size.

The DGS Scales enable one to adjust the instrument gain to an appropriate value at which the amplitudes of various sizes of disc shaped discontinuities and their changes with respect to increasing distance from the test surface, are plotted as curves. In actual use, after the preliminary adjustments of the instrument range and gain, amplitude of an indication from an unknown discontinuity can be read as the equivalent size (diameter) of a circular shaped discontinuity.

Direct echo amplitude evaluation, without the use of reference blocks containing artificial defects and faster speed of testing are, the main advantages of using a DGS Scale. As the instrument settings are specific and controlled, the results are also reproducable. Either the back wall echo from the test object (with plain parallel surfaces) or from V1N2 blocks can be used for initial setting of the instrument.

Each DGS Scale is meant for use with a specific Series II probe. They are presently available for normal and angle beam probes of 2 MHz & 4 MHz, frequency. The Scales are grouped in four basic sets.

The DGS Scales are available in two sizes each matching the instrument CRT size. DGS Scales type DGS-EN, DGS-ENM, DGS-EA, DGS-EAM are suitable for instrument with CRT size 70 x 55 mm corresponding to model ESM2 / ESM2M / ESM2MT / PX-10 / PX-20 / ED-1 equipments.

DGS Scales type DGS-ENX, DGS-ENMX, DGS-EAX, DGS-EAMX are suitable for instrument with CRT size 100 x 80 mm corresponding to model PX-001 / ESM3 equipments.

The Range of available Scales is as follows:-