HP 35s Scientific manual , 

4 ⎟ [14 + (7 ⋅ 3) – 2]

by starting with the innermost parentheses (7 ⋅ 3) and working outward, just as you would with pencil and paper. The keystrokes were 

.

If you work the problem from left–to–right, press

.

This method takes one additional keystroke. Notice that the first intermediate result is still the innermost parentheses (7 ⋅ 3). The advantage to working a problem left–to– right is that you don't have to use to reposition operands for noncommutative functions ( and ).

However, the first method (starting with the innermost parentheses) is often preferred because:

It takes fewer keystrokes.

It requires fewer registers in the stack.

Note	When using the left–to–rightmethod, be sure that no more
	than four intermediate numbers (or results) will be needed at
	one time (the stack can hold no more than four numbers).

The above example, when solved left–to–right, needed all registers in the stack at one point:

Keys:	Display:	Description:
		Saves 4 and 14 as intermediate
		numbers in the stack.
	_	At this point the stack is full with
		numbers for this calculation.
		Intermediate result.
		Intermediate result.

RPN: The Automatic Memory Stack 2-15