Update 3/19/16: To make this actually usable, it no longer uses Customizer! All files to create it are now in the archive as well. I hope this helps everyone build this cool little sundial.
Customizable Horizontal Sundial. Use Customizer to specify your location and give your dial a custom label! Note that the dial is corrected to read in Standard Time for your Time Zone.
Update 3/19/16:Here are detailed instructions for editing the OpenSCAD file to build your custom version (avoids Customizer woes). For those in the Southern Hemisphere, it might be as simple as entering your latitude as a positive number (as though it were for the Northern Hemisphere). I'm not certain, but I think you will get a usable sundial. Please post your results one way or another.
Caveat: This sundial is designed for the Northern Hemisphere. I have no clear idea how to adapt it to the Southern Hemisphere yet. When I figure that out, I'll post a Southern Hemisphere version.
The Horizontal Sundial is easily customized to your location. Start by finding your latitude and longitude (in decimal degrees) here: http://universimmedia.pagesperso-orange.fr/geo/loc.htm
Longitude may be positive or negative; Latitude will be positive. (Otherwise you're in the Southern Hemisphere. Refer to the Caveat above, but maybe just change the sign.) Note you must indicate both your exact Latitude as well as the range of your latitude in degrees (Works the same for the Southern Hemisphere once you change the sign). This is because of an OpenSCAD limitation.The comments in the OpenSCAD code explain how to determine the range value.
Then find your time zone correction here: http://www.timeanddate.com/library/abbreviations/timezones/ There are many different names for time zones. At the site, simply use Find in your browser to look up the correction for your time zone.
Now use Customizer to enter your data and make an awesome custom sundial!
Update 3/19/16: Forget using Customizer. Download the file HorizDial.scad. Also download Write.scad and Letters.dxf. All three files should go in the same directory. (You can also get the Write package here http://www.thingiverse.com/thing:16193/#files , but the version I provide is known to work with HorizDial.scad and removes the annoying "ECHO" statements.)
Use OpenSCAD to edit HorizDial.scad and produce the stl file. (The latest version of OpenSCAD as of 3/19/16 is known to work.) You'll only need to modify the values for myHome (note 21 character limit!), latitudeRange, latitude, longitude, and timeZone.
Hope this helps everyone!
Note: Although there are other sundials on Thingiverse, this one was created from scratch to be customizable.