Question

I have created a class module for an entity called Terminal. I have a method that populates this class by going through 175 seperate worksheets and pulling the correct data from specific cells. This process is very quick (about 2 seconds), however when I try to write this data back out to a new worksheet, it is taking much longer (45 seconds). It would seem that this process should be atleast as fast as populating the class since it never has to leave the worksheet, however, it is not. Below is the process that I am using to write the data to the worksheet, am I overlooking something that is causing this to run so slowly?

Application.ScreenUpdating = False
 Dim rowNumber As Integer
 Dim colNumber As Integer
 Dim terminalCode As String
 Dim terminal As clsTerminal

 rowNumber = 7
 colNumber = 1

 For Each terminal In terminals

        'Add hyperlink to each terminal code
        Sheets("Terminal Summary").Hyperlinks.Add Anchor:=Cells(rowNumber, colNumber), Address:="", _
            SubAddress:=terminal.terminalCode + "!A1", TextToDisplay:=terminal.terminalCode

        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 1).Value = "Current"

        'Current period
        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 2).Value = terminal.iBShipments
        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 3).Value = terminal.oBShipments
        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 4).Value = terminal.iBNetRevenue
        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 5).Value = terminal.oBNetRevenue
        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 6).Value = terminal.iBWeight
        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 7).Value = terminal.oBWeight
        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 8).Value = terminal.iBMileage
        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 9).Value = terminal.oBMileage
        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 10).FormulaR1C1 = "=IFERROR(RC[-4]/RC[-8],0)"
        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 11).FormulaR1C1 = "=IFERROR(RC[-4]/RC[-8],0)"
        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 12).FormulaR1C1 = "=IFERROR(RC[-8]/RC[-10],0)"
        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 13).FormulaR1C1 = "=IFERROR(RC[-8]/RC[-10],0)"
        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 14).FormulaR1C1 = "=IFERROR(RC[-10]/(RC[-8] / 100),0)"
        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 15).FormulaR1C1 = "=IFERROR(RC[-10]/(RC[-8] / 100),0)"
        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 16).FormulaR1C1 = "=IFERROR(RC[-12]/RC[-8],0)"
        Sheets("Terminal Summary").Cells(rowNumber, colNumber + 17).FormulaR1C1 = "=IFERROR(RC[-12]/RC[-8],0)"

        rowNumber = rowNumber + 1
    Next terminal

Edit
I should have noted terminals is a collection of the terminal class

Answer 1

A common pitfall with this type of code is that every time you write data to the spreadsheet, Excel runs through a calculation (it evaluates all of the formulas in the workbook to see if they need to be computed with the new data).

If you disable automatic calculation before your loop and then re-enable it afterwards, things will move much quicker:

Application.Calculation = xlCalculationManual
For Each terminal In terminals
...
Next terminal
Application.Calculation = xlCalculationAutomatic