Section 3: Automatic Memory Stack and ALPHA Register54
Example. A bacteriologist tests a certain strain whose population typically increases by 15% each day (a growth factor of 1.15). If he starts a sample culture of 1000, what will be the bacteria population at the end of each day for five consecutive days?
Method: Put the growth factor (1.15) in the Y-, Z-, and T-registers and put the original population (1000) in the X-register. Thereafter, you get the new daily population whenever you press  × .
Keystrokes Display    
1.15  1.15 _   Growth factor.
ENTER    1.15000    
ENTER    1.15000    
ENTER    1.15000   Growth factor is now in T.
1000  1000 _   Starting population.
 ×    1,150.0000   Population after 1st day.
 ×    1,322.5000   Population after 2th day.
 ×    1,520.8750   Population after 3th day.
 ×    1,749.0063   Population after 4th day.
 ×    2,011.3572   Population after 5th day.
When you press  ×  the first time, you calculate 1.15 × 1000. The result (1,150) is displayed in the X-register and a new copy of the growth factor drops into the Y-register. Since a new copy of the growth factor is duplicated from the T-register each time the stack drops, you never have to reenter it.
Notice that performing a two-number operation such as  ×  causes the number in the T-register to be duplicated there each time the stack is dropped. However, the R  function simply rotates the contents of the stack registers; it does not rewrite any number, but merely shifts the numbers that are already in the stack.