Converting To Nano, Micro And Milliseconds

If the time is not less than 0.001 seconds, then multiply it by 1000, and express it in milliseconds. Otherwise: If the time is not less than 0.000001 seconds, then multiply it by 1000000, and express it in microseconds. Otherwise: multiply it by 1000000000, and express it in nanoseconds and this all has to go in a chart like this one. I was wondering what the code would be to get this

Sub MAcro3()
Function secnum(seconds)

If seconds > 0 Then
secnum = seconds
Else
Milliseconds = seconds / 1000
If Milliseconds > 0.001 Then
Value (Substitute(0.001, 0.001 * 1000))
secnum = Milliseconds
Else
Microseconds = seconds / 1000000
If Microseconds > 0.000001 Then .............