You are downloading the G3Calculator AppX file v188.8.131.52 for Windows Phone. G3Calculator is a free and useful Productivity app: This is not just a calculator. There's more to it than just the cover. If you're not aware of what more there is then it isn't recommended you ... You can now download the offline AppX file to install & try it.
Download Locations for G3Calculator 184.108.40.206 AppX file
Important Notice: Now Due To Unspecified Limitations, You Can Not Use The Offline AppX File To Install It Any More.
To try to install it manually from an SD card, you should choose one of the server location above to get the offline G3Calculator AppX file, move the file to your phone's SD card and then tap 'Install local apps' in the phone's App list.