• Zero tick plus is when a security is transacted above the national best offer (aptic) and then another transaction occurs at the same price.

  • Up until 2007, the Securities and Exchange Commission (SEC) operated under the rule that stocks could only be shorted on a rise or a zero plus tick to prevent the stock from destabilizing.
  • Since 2010, the alternative up rule has been that if stocks are down more than 10%, intraday traders can only go short on the up. They are free to go short as long as the stock does not fall more than 10%.