May 2 (GMM) Sauber was the team with the biggest update package as F1's ultra-rare in-season test began on Tuesday.
Kamui Kobayashi was in charge of the revised C31, which including a new exhaust and front wing represented "the biggest update package" of all the teams at Mugello, according to Germany's Auto Motor und Sport.
It was a similar story in the Mercedes camp.
Williams' Valtteri Bottas, however, was in charge of testing a new McLaren-like exhaust for the FW34, while Ferrari also has a new exhaust for the F2012.
On Thursday, as the three-day test wraps up, the famous Italian team will debut other developments, including a new engine cover and sidepods.
A new front wing, nose and floor will only be ready for Barcelona.
There were no radical modifications on display by Red Bull, who instead want to use the Mugello test to work on car setup.
"We still need to learn how to get the most from what we have," confirmed Bahrain winner Sebastian Vettel.
For that purpose, the Ferrari-owned Mugello circuit might not actually be the best venue.
"It's great for driving," said Mercedes' Nico Rosberg, "but for the engineers Barcelona would be a bit better because there are all types of corners.
"At Mugello they are mainly fast, and virtually none at low speed."