A pretty basic upgrade overall.
In 1980, motor vehicles in America came with a rather annoying 85mph speedometer thanks to federal regulations.
This practice was later dropped, and only a few short years worth of bikes were sold with this strangulated and laughable attempt at speed and fuel consumption control.
Unfortunately, the Seca Turbo fell within that era, and we have lived with that curse ever since. The one bright side of the tale is that no other country was stupid enough to try this tactic, so we American owners can simply locate a Speedo from outside our borders.
In my case, fellow UK Seca owner Garry stepped up and found me a new International gauge (Our UK brethren call it a Clock, which I find kinda Cool!)
With the outside digits in KPH, and the inside in MPH, it is a bit tricky to get use to, but still a vast improvement over a pegged needle!
Replacing the unit required removing the front fairing, and pulling the instrument cluster from the bike. A few screws later, the speedo part of the cluster simply lifts out from the front of the housing. (You must remove the headlight, and disconnect most of the connectors inside the bucket, to remove the cluster. This might be a good time to address any oxidized or corroded connectors you fine there.)
I choose to retain the mileage from my original speedo, and the odometer was easy to rotate by placing a thumbnail between the digits. This allowed the digit wheels to disengage from the mating gears, and spin freely.
BTW:; Here are other units seen on the Seca.