Are there any limitations on the length and type of charactors in labels?
There is no practical limitation on the length of string in a label. However, the use of single quote in a string will cause plotting errors on data refresh. The x/y grid in the chart is too dense. You can set the grid step size in the axis label dialog box (under Edit-Axis Label…) in Chart designer or use the GRID_STEPSIZE property in API.