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First, the drawings are either ISO, ANSI or ASME not SAE...
ISO - International Standards Organization
ANSI = American National Standards Institute
ASME = American Society of Mechanical Engineers
Expressing dimensional data with double minus or positive is not wrong (different maybe), this practice is very ISO btw. These tolerances may have been derived from ANSI B4.1 or ANSI B4.2 or ISO 286 (part I & II).
8.00mm (size) -.027mm,-.034mm means that the feature (with or without size) should be as-manufactured between 7.973 and 7.966. There is not a "desired size or distance" simply a range of acceptable sizes or distances.
If you have a ~need to rewrite the size and tolerance expression for a bi-lateral equal tolerance - have at it, however the end item should be manufactured within the same dimensional range or limits.