The Automatic Memory Stack
69
Example: A bacteriologist tests a
certain
strain
whose population
typically increases by 15% each day.
If he starts a sample culture of 1000,
what will be the bacteria population at
the end of each day for six 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 population whenever you press £3 .
Press
Display
1.15
Growth factor.
Growth factor now in T.
1000
1000.
Starting population.
1150.00
Population after 15 day.
1322.50
Population after 2" day.
a
1520.88
Population after 3™ day.
8
1749.01
Population after 4day.
8
2011.36
Population after 5™ day.
a8
2313.06
Population after 6' day.
When you press &4 the first time, you calculate 1.15 X 1000. The
result (1150.00) 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 reenterit.
Notice that performing a two-number operation such as EJ causes
the number in the T-register to be duplicated there each time the
stack is dropped. However, the (R¥) key, sinceit rotatesthe contents of
the stack registers, does not rewrite any number, but merely shifts
the numbers that are already in the stack.