Suppose that you've purchased a commercial sundial and you want to make it work correctly for your latitude.  Further, you don't live on your time zone meridian, but are some kilometers/miles east or west of that longitude line. 

Steve Lelievre has written a web app that allows you to build a wedge to hold the sundial.  You can use the calculator to simply make a latitude wedge to compensate the dial latitude and your latitude, but Steve's app does a lot more.  It corrects for you longitude by performing two rotations: (1) the dial is rotated by a specified angle on the face of the wedge, then (2) the whole dial and wedge are rotated by a second specified angle.

The result is that your sundial wll now tell accurate solar time at your time zone meridian!   This is a very handy calculator: Go to: https://gnomoni.ca/wedge/