var instance = new GcSpread.Sheets.Calc.Expressions.ExternalRangeExpression(source,
                                                                           startRow,
                                                                           startColumn,
                                                                           endRow,
                                                                           endColumn,
                                                                           startRowRelative,
                                                                           startColumnRelative,
                                                                           endRowRelative,
                                                                           endColumnRelative);
var value; // Type: object
value = instance.getRange(baseRow, baseColumn);