"In the first place I was trying to learn the dynamics of an F1 car, its characteristics and the way the aero works.
"It went pretty much as I expected, but that doesn't mean I didn't really enjoy it."
Armstrong has been racing karts and cars from the time he could run. Speed is not an issue for him, having driven faster machinery as he progressed through the categories, most recently into F2 last year.
An F2 car has around the same top speed as a an F1 car, but that's about the only similarity.
"It was incredibly fast and by that I don't mean top speed. An F2 car will get close to an F1's top speed at the end of the straight only about 15km/h slower, but an F1 car gets there [top speed] so much quicker. You get to 300km/h halfway down the straight; it's incredible.
"The power unit and torque developed in an F1 car is so different to anything else. Maximising an F1 car is hard with the amount of downforce and power and you don't really know where the limits are. The downforce is quite different to that of an F2 car.
"Driving the car is not the issue, it's what I've done since I was a kid. It's everything else that's going on at the same time. You have to think about tyre temperatures, brake temper-atures and your engineer is constantly talking to you on the radio about all sorts of things.
"Driving that quick is actually the simple part, the difficult part is having the spare brain capacity to think about other things that are not necessary to driving the car. As a test driver, about 30 per cent of your time you're analysing what the car is doing, remember what the car is doing and being able to explain all that to the engineers," he said.
After a fraught 2020 in F2 racing with ART Grand Prix where his season started with two podium finishes only to fall away dramatically for the rest of the season.
Armstrong is looking forward to this season with a clean slate as he has signed with DAMS in the F1 feeder series.
"I'm happy to have a change of scenery. I'm with [French team] DAMS now. We have clear targets now and I feel much more confident this year and they know what they want. You've got to know what you're the expectations are if you want to win.
"I'm quietly confident," said Armstrong of the season ahead.