Consider doing following items at a same time:
- Calculate a value.
- Fix decimal numbers maximum at two places (or maybe round).
- Always use sign in prefix (In another meaning always "+", in case of negative numbers switch to "-").
- Which unit is it? Add it as a suffix.

I only know this way so far:
Code:
MyLabel.Text = String.Format("+0.00", MySingleVariable / 1000) 'is ToString needed?
'If/Else reguired for desission making whether UnitA or UnitB is required.
I'm sure Visual Studio developers are already dedicated a shortened, magical, one-lined, command for it cause they've encountered and struggled with this difficulty before.

(Not familiar with below structure: I'm not sure is it helpful or not)
Code:
MyLabel.Text = MySingleVariable.ToString(Format As String, Provider As IFormatProvider)