There are some details on the front wing and exhaust "not seen" elsewhere in the 2013 field.
Feb.19 (GMM) Williams on Tuesday completed the 2013 grid by finally launching its new FW35.
Every other team got their cars up and running recently at Jerez, triggering many rumours and whispers about the reason for the Oxfordshire team's delay.
And he said the location of the first test was another reason.
"As a test track, Jerez is not very meaningful -- you can really only do system or reliability checks.
"The serious testing starts here in Barcelona," he is quoted by Germany's Auto Motor und Sport.
The publication's correspondent Michael Schmidt said the FW35 is "not a sensation", but there are some details on the front wing and exhaust "not seen" elsewhere in the 2013 field.
Indeed, he said Coughlan's Coanda exhaust solution enters "the grey areas of the regulations".
Caterham has similarly raised eyebrows with its 2013 solution, and Coughlan on Tuesday admitted he is one of those who thinks the green car might not be legal.
But he told Auto Motor und Sport his solution for the FW35 "adheres to the rules".