1. The LinearAxis has a LabelFormat property. By default, the chart calculates the labels with a G7 label format and this is why you get the 25E+06 formatting. You can set the LabelFormat to a format that fits your requirements, such as G20.
2. It seems that you are creating several label definitions. The series will produce a label for each definition you have. So if you add 10 definitions, and if you have 5 data points - then each five data points will have 10 labels to it, hence 50 labels in total. So make sure you only add one definition per series, in order to get one label per point.
Even though you are currently doing some things in code behind - I think you should try using the SeriesProvider, which was built with the purpose of creating dynamical number of series. References here
QSF example which uses the SeriesProvider
SeriesProvider SDK sample
Let us know how it goes.
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