All of the frames in the Stack can be viewed by means of the Up and Down Arrow Keys. You can go straight to the top frame by pressing Control+Up, and to the bottom frame by pressing Control+Down. F3 or the equivalent View menu item brings up a list of Frames click on one to make it visible and Active.
If you are viewing a Frame, or can view it by pressing Tab or O (see below), this frame is called the Active Frame. Several functions use this Frame either as input or as a reference point.
Pressing 'G' will goto the Frame who's pixel is at the location being pointed at by the mouse. It makes no difference what is on the screen, it's the pixel in the Picture at this location that counts.
If you press '.' (Dot or Point) whatever is the Active Frame also becomes Active Frame 2. On the Title Line these Active Frames are abbreviated A1 and A2. A2 is used in some functions that require 2 Frames to work on, and also when comparing two frames.
+ will toggle between the Active Frame and Active Frame 2, A1 and A2. This is useful when comparing multiple frames output by a macro.
The Tab key is a toggle key. It switches from a view of the Active Frame to one of the Picture.
O is a toggle key also. It switches from a view of the Active Frame to one of Out which is where the results of several operations are stored.
Several of these keystrokes have menu equivalents on the View menu.
1, 2, 3, and 4 set Points on whatever Frame is Active at the time, and Control+ these keys will go directly to the frame containing the corresponding Point.