Arithmetic with times

Hi i have two times in the format mm.ss (minutes.seconds)

I want to subtract 1 minute and thirty seconds from 30 minutes eg. x = 30.00 - 1.30

If i did that normally the result would be 28.7

I of course want the answer to be 28.30

Are there any mathematical genii out there who can help me?

Thanks in advance, John

VB Code:

Private Function TimeDiff(ByVal strTime1 As String, ByVal strTime2 As String) As String
        Dim sMinutes As Short = Split(strTime1, ".")(0) - Split(strTime2, ".")(0)
        Dim sSeconds As Short = Split(strTime1, ".")(1) - Split(strTime2, ".")(1)
 
        sSeconds = sMinutes * 60 + sSeconds ' Convert Value to seconds
 
        'now convert back to minutes.seconds
 
        sMinutes = (sSeconds - (sSeconds Mod 60)) / 60
        sSeconds = (sSeconds Mod 60)
 
        Return sMinutes & "." & sSeconds
 
 
    End Function

Use the TimeSpan object to work with time calculations:

VB Code:

Dim ts As New TimeSpan(0, 30, 0) 'start with 30 min
        MsgBox(ts.Subtract(New TimeSpan(0, 1, 30)).ToString) 'subtract 1 min 30 sec

You can enter the time as a string too if you prefer, just use the parse shared method.

VB Code:

ts = TimeSpan.Parse("0:30:00")
        MsgBox(ts.Subtract(TimeSpan.Parse("0:01:30")).ToString)

I am testing performance and comparing time concumprtions in Java and .net and for this I need to calculated in milliseconds. My timestamps are:

time1 = Now.Hour & ":" & Now.Minute & ":" & Now.Second & ":" & Now.Millisecond

when the calculation begins and

time2 = Now.Hour & ":" & Now.Minute & ":" & Now.Second & ":" & Now.Millisecond

How do I subtract the two times when I need milliseconds?