What is 3-2-3 gauge accuracy and how is it different from full scale accuracy?

PRESSURE GAUGE ACCURACY

The accuracy is the difference (error) between the true value and the indication expressed as percent of the span. It includes the combined effects of method, observer, apparatus, and environment. ASME B40.1 and DIN accuracy grades are frequently used:

Grade 4A (0.1% Full Scale)
Grade 3A (0.25% Full Scale)
Grade 2A (0.5% Full Scale)
Grade 1A (1% Full Scale)
Grade A (1% middle half, 2% first and last quarters)
Grade B (2% middle half, 3% first and last quarters)
Grade C (3% middle half, 4% first and last quarters)
Grade D (5% Full Scale)

In cases where the accuracy differs between the middle span and the first and last quarters of the scale, the largest % error is reported.