Hi Henry,
Thanks for evaluating Syncfusion products.
Display 4 Decimal place in y-axis I am afraid that I was not able to reproduce the issue. When I set the this.ChartWebControl1.PrimaryYAxis.Format = "0.0000", it displays only 4 decimal places. I have tested this issue in version 6.1.0.34.
Please download the sample from the below location: