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BA II PLUS™ Calculator
Accuracy Information
Internally, the calculator stores results as 13-digit numbers. In
the display, however, results are rounded to 10 digits or fewer,
depending on the decimal format. The internal digits, called
“guard” digits, increase the calculator’s accuracy. Any later
calculations are performed using the internal value, not on the
value in the display.
Rounding
If a calculation produces an 11-digit (or greater) result, the
calculator uses the internal guard digits to determine how to
display the result.
If the eleventh digit of the result is 5 or greater, the calculator
automatically rounds the result to the next larger value for
display.
For example, consider this problem.
1
P
3
Q
3 = ?
Internally, the calculator solves the problem in two steps, as
shown below.
1. 1
P
3 = 0.3333333333333
2. 0.3333333333333
Q
3 = 0.9999999999999
The calculator rounds the result and displays it as 1. This
rounding enables the calculator to display the most accurate
result.
Most calculations are accurate to within ±1 in the last displayed
digit. However, higher-order mathematical functions use
iterative calculations, and inaccuracies can accumulate in the
guard digits. In most cases, the cumulative error from these
calculations is maintained beyond the 10-digit display so that no
inaccuracy is shown.
