Updated with correct information from the smogon research thread
When the Poké Radar is used, the game generates four "rings" around the player, with the first ring consisting of the eight squares surrounding the player, the second ring consisting of the 16 squares surrounding the first ring, and so on for the third and fourth rings. One random square in each ring will be selected, and if that square is a patch of grass, that patch will shake. Therefore, the maximum number of patches that can shake with each use of the Poké Radar is four; if fewer than four patches shake, then one or more of the randomly selected squares were not patches of grass. If all four squares did not contain grass, then the game will display the message "''The grassy patch remained silent...''" and the chain will automatically break.
The patch in the farthest "ring" is the most likely to continue a chain.
Different formations of grass patches indicate different likelihoods of continuing a chain.< !-- Add Smogon reference link later-->
If a [[Pokémon outbreak|swarm]] ends while a chain is in progress, or a Pokémon otherwise ceases to become available, then that Pokémon will continue to be available until the chain is broken.