This sundial is meant to be positioned on the outside of a sun-oriented window. It's shadow falls on a half transparent layer that can be read from the inside and the outside of the house.

This sundial will work nicely on the moderate latitudes on the Northern hemisphere. I expect it to work on the moderate latitudes in the Southern hemisphere too (please give feedback on that) .

For this sundial some thoughts have been leading:

• The dial is more or less (±60°) orientated towards the sun at noon;
• The 'sun revolves' in 24 hr around in a plane perpendicular to the Earth' rotation axis.
• The elevation of the sun at its highest point may vary through the year;
• The gnomon can be made as thick as desirable without distorting the time reading.

Since the dial depends on your specific location and orientation on Earth, the attached stl's are only examples and are useless for your specific needs. You'll have to generate your specific model with OpenSCAD yourself.
This is not difficult!

• Download verticalSeeThroughSundial.scad from thingiverse.com (and remember the download location);
• Download the OpenSCAD installer from www.openscad.org;
• Run the installer (and remember the installation directory (for me (Win10): C:Program FilesOpenSCAD)
• Run openscad.exe from this directory;
• Open the file verticalSeeThroughSundial.scad in OpenSCAD;
• Adapt the variables 'myLatitude', 'myLongitude', 'myTimeZone' and 'mySundialFacingAngle' for your own situation. Instructions on how to find the correct values are in the source text;
• Generate your own sundial bij rendering it (F6 or 'Design|Render'). This will take a few minutes (watch the progress bar down right);
• Export the sun dial as a stl-file (F7 or 'File|Export|Export as STL...' ). Chose an appropriate directory and filename;
• Use this stl-file as input for your slicer program.