Why would anyone? You simply scrub the numeric position field with multiple layers selected to get relative adjustments. Basics of AE.
(A less condescending answer would be nice.)
How do you add 1.85 by scrubbing? It's imprecise.
You can always select the value in the timeline then move the cursor to the end with the right arrow key and then type + 1.85
Math functions work in most places where you can type in a value. For example:
You can also look at the info palette as you drag layers around with the tools, here I have changed the angle - 16.2 degrees
You can see rotation, scale and position changes in the info palette, the top value is the current value, the second shows the change from the original.
For precise dragging you can hold down the Cmnd/Ctrl key to increase accuracy by a factor of 10 or hold down the shift key to make the values increase 10 times as fast.
To alter position, I'd just hightlight all the keyframes in question, park the timeline cursor on one of those keyframes, then use the left-right-up-down arrow keys. Want multiples of ten? Hold down the shift key as you hit the arrow key. Then it becomes a simple mattter of counting.
Arrow keys only work with position, but I need a solution for any keyframe stream. Entering equations into the numeric entry doesn't work when moving multiple keyframes, since it still sets every keyframe to that value. If the value is 10 and you enter "10+20", it doesn't add 20 to every keyframe, it just sets every keyframe to 30. It would be perfect if it let me type in "n+20", and then evaluated the expression for each keyframe to set its new value, but no such luck.
As for number scrubbing, there are countless problems, even ignoring the lack of precision. You can't drag by just 1; it doesn't start changing until the cursor has moved a minimum distance, so it doesn't move at all and then suddenly jumps to +3. (That's normal dragging behavior--it's so you don't accidentally drag when you're just trying to click--but it makes this interface hard to use.) You also can't easily see the number you're changing (the mouse cursor is covering it!), and if you have an expression on the field you can't see the initial value at all, since it shows the result value until it sees a drag, not the source value.
- Select a bunch of position keyframes, run the script, and enter "n += 50" to add 50 to the X position of all selected keyframes.
- Select slider control keyframes, and "n++" will increase them all by 1.
- Select scale keyframes, and "n *= 2; n *= 2; n *= 2;" to double the scale of all of them.
- "n = Math.round(n); n = Math.round(n);" will snap selected keyframes to the nearest integer.
- Select rotation keyframes, and "n += 90" will add 90 degrees to all of them.
- Select checkbox keyframes, and n = !n will flip them all.