Why the data retrieved by the PI Datalink in the Excel is not the same as the data in the archive editor?

SMT is rounding. I don't know how to change the automatic formatting. Excel should be showing the "real value" for as many decimal points you tell it to show.

SMT is rounding. I don't know how to change the automatic formatting. Excel should be showing the "real value" for as many decimal points you tell it to show.

This is not correct. SMT is not rounding. Rather, Excel has introduced artificial and meaningless digts.

If the tags are Float32, then SMT is correctly showing the single-precision floating point value. Excel on the other hand, will show the value as double-precision, which means the cast from single to double introduces extra digits. This is a well-known artifact of IEEE 754 floating points.