I believe @Erik the Awful posted a Youtoob video he made going over how to check torque wrenchs. Not sure what thread its in but should be findable if you take the dive.
Edit: here -> Post in thread 'Question about torquing the heads.' https://www.gmt400.com/threads/question-about-torquing-the-heads.60516/post-1284121
Edit: here -> Post in thread 'Question about torquing the heads.' https://www.gmt400.com/threads/question-about-torquing-the-heads.60516/post-1284121