It could be as simple as looking on the property sheet format tab for the control and switching it from Auto to the number of decimal places you want to see, as long as you have the format on the format tab set to something that supports this, such as Fixed or Standard. I'd try that first.
Otherwise, AFAIK, what you're asking for has to be done with vba. If your control is bound to a field and you try to do =Format([SystemID],"#,##0\].\[00") in the control itself, you will get either #Error, #Name or #Type as a result. In vba, if you apply a format to a bound field and for example, format 12.1234 to 1 decimal place, you will actually change the value in the table to 12.1. The vba route would be typically used with unbound fields. I strongly suggest using the property sheet.