HP 48gII - Manual (Page 282)

Page 9-7
The following screen shots show the RPN stack before and after applying
function ARRY:
In RPN mode, the function [
→ ARRY] takes the objects from stack levels n+1, n,
n-1, …, down to stack levels 3 and 2, and converts them into a vector of n
elements. The object originally at stack level n+1 becomes the first element,
the object originally at level n becomes the second element, and so on.
Note: Function ARRY is also available in the PRG/TYPE menu („°)
Identifying, extracting, and inserting vector elements
If you store a vector into a variable name, say A, you can identify elements of
the vector by using A(i), where i is an integer number less than or equal to the
vector size. For example, create the following array and store it in variable
A: [-1, -2, -3, -4, -5]:
To recall the third element of A, for example, you could type in A(3) into the
calculator. In ALG mode, simply type A(3). In RPN mode, type ‘A(3)’
`µ.
You can operate with elements of the array by writing and evaluating
algebraic expressions such as: