Our coordinate calculations spreadsheet enables you to carry out common calculations with coordinates. It includes a full set of Transverse Mercator projection functions, which allows you to: The document opposite is the user manual for the calculations you can perform using the spreadsheet. It explain the limitations of this type of datum transformation, which you should bear in mind. For example, if you need accuracy greater than the nearest 5 metres, you should use OSTN02 and OSGM02 on the surveying guidance page, rather than the simple conversion GPS to National Grid conversion requiring better than 5-metre accuracy, you should not use the simple transformation calculated by the spreadsheet. Note: Projection functions such as scale factors, convergence and t-T are included in the spreadsheet but not in the guide. Source.