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In
addition
,
the
~
key is used to
compute
the
sum
of the squares
of all
your
entries, and
keeps
track of
the number
of
entries
you've
made.
(To
see
how many entries you've made,
simply press
x:y
.
But
before you resume
summing
press
x:y
again.)
The mean is
calculated
by
pressing.
;
the altern ate
function
of this
key
•
permits you to
continue summing-thereby modifying the
results
of previous
mean
calculations.
We've
also
provided
an
error recovery routine in
case
incorrect data
is
entered.
To
correct your
last entry calculation,
after
pressing
~,
!-
reenter the
incorrect value
and press
~
;
you
are
back where
you
were
before
the incorrect
entry. Note
that
a value
must be
entered
prior
to
each
~
keystroke or errors will
result.
Sum-ot-Digits Calculations
The sum-of-the-digits
key
Ell
is used to
calculate
an
amortization
schedule and related balances
for consumer finance charges
or depre-
ciation of capital assets.
Amortization
on a
period-by-period
basis
as
well as the remaining
balance
after
any
given
period can be
obtained.
Furthermore, you have
the option
of
finding this information
at
any point in the
amortized
life
span and can obtain values
for all subsequent
periods
if you wish.
Trend Line Calculations
To
forecast or estimate
trends,
you may
chart
a straight
line of best fit
through
data
points across
a periodic
(daily,
weekly, etc.)
time
span
.
This
type of
analysis
is
made
possible
through
the
III
(trend
line)
key.
The
HP-80
calculates
the
course of a
straight trend line by operating
on
chronologically-entered
data,
and
then projecting the line to any
point.
24
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