The pot is split between the player with the best hand and the player who has the LOWEST spade card face-down. The dealer who calls this game needs to specify whether or not the Ace of Spades will be counted as the lowest spade card, or whether it is the Two of Spades. This is a discrepancy because the Ace is typically considered the highest card of the suit, but nevertheless, it can be used to make a straight from Ace to five and is therefore, a low card. When I call Low Chicago, I call the Ace of Spades as the lowest possible spade card and not the two.
The exact same rules apply except in this game, the pot is split between the player with the best hand and the player who has the HIGHEST spade card face-down.