Scaling and units
Every conversion point should use the intended lower/upper range and engineering unit. Duplicate conversions can be especially dangerous: a value may be scaled once in an input module and a second time in software.
Quality/status flags
Digital systems can carry information about bad, uncertain, substituted or stale values. Applications should not silently display such values as if they were current high-confidence measurements.
Timestamps
Event sequence analysis depends on synchronized time sources and an understood timestamp origin. A historian timestamp may represent source time, server receipt time or another processing point.
Metadata
Useful metadata includes tag, description, unit, range, sensor type, location, calibration status and source system. Without it, a numeric time series loses much of its meaning.
Configuration change control
Range, unit and damping changes should be controlled because historical trends may otherwise appear to shift or become incomparable. Configuration backups and audit trails help explain changes.