add two manuals and a video

README.md

@@ -187,6 +187,7 @@ Blog posts, articles, tutorials, galleries, videos, et cetera.
 - [What is a pen plotter 2022?](https://www.youtube.com/watch?v=J1NpYzETm3M) - Nice video introduction to modern plotters in 2022.
 - [Tools, Tricks, and Hacks: Exploring Novel Digital Fabrication Workflows on #PlotterTwitter](https://dl.acm.org/doi/abs/10.1145/3411764.3445653) - Research paper on the novel workflows of the plotter community ([Video Summary](https://www.youtube.com/watch?v=xqhT-8ElJ68)).
 - [Orbis Tertius](https://www.glkitty.com/pages/orbistertius.html) - An immersive digital installation with plotter output of Martian topography.
+- [Tech Tangents: Plotting For The First Time - HP 7470A](https://www.youtube.com/watch?v=tk4c4WMZJZ8) - Nice video showing an HP 7470A operated from an HP 85 computer.
 
 ## Manuals and Ephemera
 
@@ -207,6 +208,8 @@ Scanned plotter manuals and marketing ephemera, mostly from the [Internet Archiv
 - [Houston Instrument HIPLOT DMP-51/52 Operation Manual (1985)](https://archive.org/details/hi-dmp-51-52-operation-manual)
 - [Houston Instrument Interface Notes for DM/PL Intelligent Plotters (1983)](https://archive.org/details/hi-interface-notes-dm-pl-plotters)
 - [Houston Instrument Stand Assembly Procedure DMP-50 Series Plotter](https://archive.org/details/hi-stand-assembly-procedure-dmp-50-series-plotter)
+- [HP 7470A Interconnection Guide](https://archive.org/details/manualzilla-id-7029812)
+- [HP 7470A Operator's Manual (manualslib)](https://www.manualslib.com/manual/1089592/Hp-7470a.html)
 - [HP 7475A Graphics Plotter Operation and Interconnection Manual](https://archive.org/details/HP7475AOperationManual)
 - [HP 7570A DraftPro Plotter Hardware Support Manual](https://archive.org/details/7570adraftproplotterhardwaresupportmanual0757090000201pagesdec86)
 - [HP 7585B Drafting Plotter Service Manual (1983)](https://archive.org/details/bitsavers_hpplotter0_18190273)