While the team's Spa upgrades ran smoothly, there's still some more work to do to dial in the car ahead of qualifying according to Silver Arrows Trackside Engineering Director Andrew Shovlin.
"The car is working pretty well, the drivers are quite happy with it on a single lap," said Andrew. "The day was obviously affected by the rain at the end of the second session.
"We were not expecting it early on but then as the session progressed you could see the weather coming in. So we were trying to bring the programme forward a bit, as other teams were too. That has left us missing a bit of tyre data that we would normally have.
"We had new power units in the car which have been signed off well and we also brought our low-downforce package for this circuit which has performed in line with expectations.
"Overall, the drivers are reasonably pleased with the car but there are a few more unknowns than normal. We will work hard overnight to try and improve the car and fix the few issues that we've found in terms of the handling today."