sheet.gs

function lastValues(column, num, dateTime) {
  var lastRow = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Sheet1").getMaxRows();
  var values = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Sheet1").getRange(column + "1:" + column + lastRow).getValues();

  for (; values[lastRow - 1] == "" && lastRow > 0; lastRow--) {};

  arr = [];

  for(i=0; i < num+1; i++){
    arr.push(values[lastRow - i]);
  };

  return arr;
};

function onOpen() {
  var sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Sheet1");
  var entries = [{
    name : "Refresh",
    functionName : "refreshLastUpdate"
  }];
  sheet.addMenu("Refresh", entries);
};

function onEdit(e)
{
  SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Sheet1").getRange('K1').setValue(Math.random());
}

function refreshLastUpdate() {
  SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Sheet1").getRange('K1').setValue(Math.random());
}
Logger.log(SpreadsheetApp.getActiveSpreadsheet().getId());