Here's a section of the NYSE Direct + rule. I think the 1 by 1 is way to much abused, kinda like a panic button for the specialist to turn off auto ex's while he changes his quote.
NYSE DIRECT+: RULES GOVERNING AUTOMATIC EXECUTION OF LIMIT ORDERS OF A SPECIFIED SIZE
Rule 1000: Automatic Execution of Limit Orders Against Orders Reflected in NYSE Published Quotation
Only straight limit orders without tick restrictions are eligible for entry as auto ex orders. Auto ex orders to buy shall be priced at or above the price of the published NYSE offer. Auto ex orders to sell shall be priced at or below the price of the NYSE bid. An auto ex order shall receive an immediate, automatic execution against orders reflected in the Exchangeâs published quotation and shall be immediately reported as NYSE transactions, unless:
(i) the NYSEâs published quotation is in the non-firm quote mode;
(ii) the NYSEâs published quotation has been gapped for a brief period because of an influx of orders on one side of the market, and the NYSEâs published quotation size is one hundred shares at the bid and/or offer;
(iii) with respect to a single-sided auto ex order, a better price exists in another ITS participating market center;
(iv) with respect to a single-sided auto ex order, the NYSEâs published bid or offer is 100 shares;
(v) a transaction outside the NYSEâs published bid or offer pursuant to Rule 127 is in the process of being completed, in which case the specialist should publish a 100-share bid and/or offer;
(vi) trading in the subject security has been halted.
Auto ex orders that cannot be immediately executed shall be displayed as limit orders in the auction market.