Over the years, various iterations of Microsoft Excel have made it more difficult to install third party add-ins. The original installation instructions of CosmoCalc were pretty straightforward, as explained in the manual. For later versions of Excel, a few additional steps may be required:
  1. Visit http://cosmocalc.london-geochron.com and download CosmoCalc.xlam. PC users may find that Windows changes the extension of this file to .xls. If this happens, then rename it back to .xlam.
  2. Enable macros in the Trust Center: FileOptionsTrust CenterTrust Center Settings...Macro Settings and enable macros.
  3. Enable Developer tools: FileOptionsCustomize Ribbon and make sure the Developer and Add-ins boxes are ticked on the right-hand side of the window.
  4. Install CosmoCalc: FileOptionsAdd-InsManage Excel Add-ins Go...Browse... and navigate to the CosmoCalc.xlam file.
Don't hesitate to contact cosmocalc [at] gmail [dot] com with any questions.