I personally round symmetry that indicator is a beta version didn't bother doing any of that.  However symmetry for symmetry break there's a little art to it like anything in TA.  If a move was 3.66 points and another move was 3.7 points, would I call that a break in symmetry, NO.  I'd generally like to see a move of say 4 or 5 points.  However your example of SPX 2450, rounding to nearest 50 points is nuts.  Again it's all relative to the time frame you are following as well.  On a daily chart if the SPX had 20 point pullbacks - then I might count 25 poitns as enough for a sym break.  On a fast 3 min intra day chart, if the largest bounces intra day were 3 points, then I'd count a 4 point bounce as a symmetry break, it's all relative and that's why I said it's more common sense and feel.