Codes to Surpass "Type Mismatch"

[macky1730]

Hi. i made a form named calculator with "calculate" button for value execution from textboxes.
the textboxes have default corresponding default values in it. the first to do is press "clear" button first so that the default values disappear.

Everytime i open the form and press the "calculate" button as first action an error comes up showing "type mismatch". what code to insert so that if "calculate" be the first to be pressed a message box will appear which says "please press clear button first".

Please see attached access sample form.
here is the code inside.

thanks.

Option Compare Database
Option Explicit
Private Sub Calc_button_Click()
    Dim Label1 As Long, Label2 As Long, Label3 As Long, Label4 As Long, Label5 As Long, Label6 As Double
    Label1 = IIf(Me.cat1a.Value = "", 0, Me.cat1a.Value) * IIf(Me.cat1b.Value = "", 1, Me.cat1b.Value)
    Label2 = IIf(Me.cat2b.Value = "", 0, Me.cat2b.Value) * IIf(Me.cat2a.Value = "", 1, Me.cat2a.Value)
    Label3 = IIf(Me.cat3b.Value = "", 0, Me.cat3b.Value) * IIf(Me.cat3a.Value = "", 1, Me.cat3a.Value)
    Label4 = IIf(Me.cat4b.Value = "", 0, Me.cat4b.Value) * IIf(Me.cat4a.Value = "", 1, Me.cat4a.Value)
    Label5 = IIf(Me.cat5b.Value = "", 0, Me.cat5b.Value) * IIf(Me.cat5a.Value = "", 1, Me.cat5a.Value)
    If Me.Prod.Value <> "" Then
      Label6 = Me.Prod.Value
    Else
     MsgBox "Productivity / Unit Hour ??"
        Exit Sub
    End If
    Me.Equal.Value = (Label1 + Label2 + Label3 + Label4 + Label5) / Label6
End Sub
Private Sub Clear_button_Click()
    Me.cat1a.Value = ""
    Me.cat2a.Value = ""
    Me.cat3a.Value = ""
    Me.cat4a.Value = ""
    Me.cat5a.Value = ""
    Me.cat1b.Value = ""
    Me.cat2b.Value = ""
    Me.cat3b.Value = ""
    Me.cat4b.Value = ""
    Me.cat5b.Value = ""
    Me.Prod.Value = ""
    Me.Equal.Value = ""
    
End Sub

Sub Command16_Click()
    DoCmd.Close
End Sub