function main(
  workbook: ExcelScript.Workbook,
  applyTo: 'Workbook' | 'Worksheet' = 'Workbook') {

  let wsArr: ExcelScript.Worksheet[]; 

  //Create array of worksheets
  if (applyTo == 'Workbook') {
    wsArr = workbook.getWorksheets();
  } else {
    wsArr = [workbook.getActiveWorksheet()]
  }

  //Loop through array of worksheets
  for (let i = 0; i <= wsArr.length - 1; i++) {
  
    //Continue if merged area exists
    if (!wsArr[i].getRange().getMergedAreas()) continue;

    //Set merged area to a variable
    let mergedAreas = wsArr[i].getRange().getMergedAreas().getAreas();

    //Loop through all merged ranges
    for (let j = 0; j < mergedAreas.length; j++) {

      //Get each merged area
      let area = mergedAreas[j];

      //If merged area is 1 row and multiple columns
      if (area.getRowCount() == 1 && area.getColumnCount() > 1) {

        //Unmerge the range
        area.unmerge();

        //Apply center across selection
        area.getFormat().setHorizontalAlignment(ExcelScript.HorizontalAlignment.centerAcrossSelection);
      }

    }
  }
}