a question was raised in the Forum (or ME Clearing House) a few weeks ago regarding the interpretation of results from the Dockstader Valve Gear Simulator. I stumbled across this Link this morning. If you go to the attached Link and scroll to the bottom there is a Link to "Steam Locomotive Valve Gear Animation Videos". Click that and another List comes up. Click on the last item "Valve Event, Cylinder Event and Valve Ellipse Diagram Explanation".

The other items at that last list lead to YouTube videos made from the Dockstader program with the associated Ellipse Diagrams. On the Stepheson Link there is commentary on the Ellipse that gives the front & rear Cutoff Values so one can cross-check one is reading the Ellipse correctly.

Lake Forest Live Steamers Railway Museum (jghtech.com)

What I do not understand is, if you type in the "main http" name "www.jghtech.com" you don't get to the site. If all else fails try googling "Deerfield and Roundabout Railway". Click on the item "Deerfield and Roundabout Railway – IBLS" and then click on "official site".