Coordinates transformation accuracy

[IrenIren]

I need coordinates transformation for Point Feature Clases. Situation:

I have imported points in local projected coordinate system. Now I need to get points coordinates in geographic coodinate system. I need to have each point coordinates in attribute table. So, in attribute table I use calculate geometry function. It seems that after I calculate coodinates to geographic system (DMS), seconds parts become incorrect. Is it possible that an error accurs while making a transformation? Does anyone has any other comment on this question?

Coordinates example:

Local system: 6207549.78, 318656.45

WGS system after transformation: 21°5'41,58"E  55°58'4,13"N 

Result using different calculator: 21°5'41,64"E  55°58'4,08"N 

[JoeBorgione]

I can't remember the author, but in a Geography text book I once read:

" A map is a set of errors that have been agreed upon"

Had it hanging in my cube for years. Couldn't find the source in a google search, but this has  pretty good description:

 https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.fsl.orst.edu/pnwerc/wrb/Atlas_web_co...