@Joker No-ones been able to explain the funky backwards lines but I think you can see the VOD there on the PSI chart.   The plot X axis is road speed and the line from data logged over time plotted in time order, so the run started at 90kph then dipped back to 85kph    likely caused by operator error, you can rule out car if you have other good plots. -Wheelspin from not being strapped down well. 1 strap and not at steep angle rushed at dyno day. Or too much power applied too quickly. -starting run and not giving it more gas so dyno load drags speed down.    

Yeah I started looking at custom ones a month ago because of exactly the conclusion you came to. It’s why I posted the canbus topic. Old cars rpm reading is just counting pulses and dividing that based on the number of cylinders. Eg 2 ignition events per revolution for a 4 cylinder. Every cheap micro controller can either count pulses or the time between them so it isn’t complicated.   Newer cars the ecu runs multi coil and the rpm signal is over canbus so you have to read the canbus messages and decode them. In some cases they do have a rom pulse from the dash cluster, but if you start opening dash clusters it raises flags if you ever want to verify the odometer. Over the weekend I think I have some basic canbus reading working but before I can test I need some more parts to look after the power and now waiting on an order for that.  

I haven't watched the clip yet but I'm heading down the rabbit hole now   Audrino based system for "under $20" ("all other" commercially of the shelf items seem to be around $3-400 and yuck)    

i had a brainwave about this issue and you could be on the right path , i was looking at data on my car and noticed the fuel compensation pids and forgot about them and  i remember subaru added software instead of fixing the issue,  The fuel compensation values can be adjusted but the root cause is the pulsing in the fuel system causing surging/ stumble at around the rpm you are describing , adding bigger injectors makes it worse so i was unsure if the fuel line mod fixed this issue, i have not had it with any of my cars but have heard of this issue years ago 

At that point it's not a shift light, it's a bar-graph colour-coded tachometer.