Hi Manal,
Most likely the problem is related to the scale you're using on the X axis. By default the chart is configured to use an ordinal (categorical) scale which supports integer (exact numbers) ticks only. This is by design. You can switch to a linear numeric step if you want to enable smaller steps:
NLinearScaleConfigurator scaleX = new NLinearScaleConfigurator();
chart.Axis(StandardAxis.PrimaryX).ScaleConfigurator = scaleX;
Let us know if you meet any problems or have any questions.
Best Regards,
Nevron Support Team