Auctions, either neutral or disturbed, become fit if we either make a fit bid or we bid a suit-setter. Fit auctions remain so for the rest of the auction.

Fit bidding is the most structured and conventional of the Chilli auction types.

WestNorthEastSouth
1pass2pass
?
Fit with hearts agreed.
WestNorthEastSouth
1pass2NTpass
?
Again fit. 2NT is a fit bid in this sequence.
WestNorthEastSouth
123pass
?
2 disturbed the auction, but now that we have agreed hearts, it becomes fit and will remain so.
WestNorthEastSouth
1pass24
?
Fit. Even though 4 looks like a disturbing bid, you cannot disturb a fit auction.

NEXT: generic Chill rules