Manual Y axis data labels

Data source is related records and a related table linked by customer_IDFK

X data series is a column on this ChartData table from for 'YearDate' (each single record is for a single year, ie, 31/03/2014, 31/03/2015 and so on)

Y data series is a column on this from the child table for 'cPercentFigure' which is a calculation of ChartData::FigureA/ChartData::FigureB.  

The typical range for this averages around 60%, so I'd like the axis to be around this mark, ie 40-80, to ensure the line doesn't appear flat as it would do on a 0-100 chart.

Other data series which are on the same child table but appear on different charts are, for example 'cPercentFigure2' which would be ChartData::FigureA/ChartData::FigureC.  

The typical range for this averages around 30%, so I'd like the axis to be around this mark, ie 0-40, to ensure the line doesn't appear flat as it would do on a 0-100 chart.

The above are a couple of examples and there are further calculations which appear in other ranges to which a more flexible axis would lend itself.

ChartData table setup, very rudimentary example:

CustomerID_FK     YearDate     FigureA     FigureB     FigureC     cPercentFigure     cPercentFigure2

1                          31/03/2014   60             100                             0.6 

1                          31/03/2015   30                              100                                        0.3

Thanks

I might be able to come up with something, if I cannot, what would you recommend as a plugin?

I've seen there are several out there, and to be fair a line chart which has a defined axis and looks a little thicker/prettier than the native one would probably be enough.

Thanks