These sketches were created in version 4 of The Geometer's Sketchpad™, which was the version licensed by the Ontario Ministry of Education at the time. In the process of updating them to version 5, particularly to allow use with the Sketchpad Explorer iPad app, we noticed some discrepancies in how the sketches displayed on different machines. Interestingly, most sketches worked just fine on my Windows machine, running at 96 pixels per inch (ppi), and on my iPad, running at 72 ppi, which is also the resolution for Macs generally.
The biggest discrepancy was between two Windows machines. On one, the sketch looked like:
After a bit of frantic emailing to our always helpful Sketchpad gurus, we discovered that there is a system setting which was different. Navigating to the Display settings in the Control Panel, we could tell that the first machine had set the size of all items to more than Smaller (on a Windows 7 machine this is called 125% or 120 ppi).
You can also see the difference if you go to the System tab of Advanced Preferences in Sketchpad, which are found in the Edit menu after the Shift key is held down.
The Screen Resolution of 37.795 px/cm is equivalent to 96 ppi and should remain at that value on Windows machines, even if Reset All Preferences is clicked. If the value is something different, it can be edited on this screen and once Sketchpad is restarted, the sketch will look like what everyone else sees.
We have been using Sketchpad for a long time and had not run into this before. It makes us worry about distributing sketches that might look awful at ppi settings that we have no control over.
