About floating-point values

Like most software, AVEVA Historian uses floating-point arithmetic. Single-precision floating-point values in AVEVA Historian are generally accurate to six decimal places and double-precision values are accurate to 15 decimal places.

Sometimes casting a single-precision floating point value as double-precision, or the reverse, means that the revision does not match the original value.

Internally, AVEVA Historian uses double precision for all calculations. This can lead to slight differences in the way results are displayed.

Standard computer representations (using IEEE 754) are stored as binary and don’t precisely match human-readable representations. Because of this, rounding for a value may not be obvious to users. For example, "230.4" may be rounded to a binary number that displays as "230.39999389648437".

For more details, refer to this Wikipedia article on the IEEE 754 standard for floating-point numbers in computers: https://en.wikipedia.org/wiki/IEEE_754-1985.