HP 48gII - Manual (Page 151)

Page 3-26
To calculate a division, say, 3250 mi / 50 h, enter it as
(3250_mi)/(50_h)
`:
which transformed to SI units, with function UBASE, produces:
Addition and subtraction can be performed, in ALG mode, without using
parentheses, e.g., 5 m + 3200 mm, can be entered simply as 5_m +
3200_mm `:
More complicated expression require the use of parentheses, e.g.,
(12_mm)*(1_cm^2)/(2_s) `:
Stack calculations in the RPN mode, do not require you to enclose the
different terms in parentheses, e.g.,
12_m ` 1.5_yd ` *
3250_mi ` 50_h ` /
These operations produce the following output: