HP HP-67

Function Keys 91
For example, to calculate a sales tax of 6.5% on a purchase of
$1500:
Press Display
1500 1500.00 Base number.
6.5 Percent rate.
0 97.50 The answer.
6.5% of $1500 is $97.50.
In the above example, when £ is pressed, the calculated answer
writes over the percentage rate in the X-register, and the base number
is preserved in the Y-register.
When you pressed [ the stack contents were changed...
...from this... ...to this.
T 0.00 T 0.00
Zz 0.00 z 0.00
Y 1500.00 Y 1500.00
X 6.5 X 97.50
Since the purchase price is now in the Y-register and the amount of
tax is in the X-register, the total amount can be obtained by simply
adding:
Press Display
1597.50 Total of price and sales
tax combined.
Percent of Change
The (percent of change) key is a two-number function that gives
the percent increase or decrease from Y to X. To find the percent
of change:
1. Key in the base number (usually, the number that happens
first in time).
2. Press E0ELD,
3.
Key
in
the
second
number.
4. Press B (%cH),