Direction of scrolling for Layer 1.
#$00 = left (or up); #$02 = right (or down).
Used to index the various camera tables at $7E0045 to $7E0048 and $7E004D to $7E0050.
When handling routine $00F70D, it is set to $00 if the player's on-screen X position is less than the value of $142A and $02 otherwise. This is used to determine which side to enable spawning sprites depending which side the player is on compared to $142A.
It is also temporarily set to #$01 during level load for loading onscreen sprites.
The last screen number, plus 1 (so if a level is 2 screens wide (screens 0 and 1 are only accessible), $5E would have a value of $02) before the camera stops moving rightwards. (Only applies in horizontal levels.)