Spotlight: TI-55 from 1977
Welcome
to a special Monday Edition of Eddie’s Math and Calculator Blog.
Today,
we have the original TI-55! Thankfully, I have the AC-adapter.
Quick Facts
Model: TI-55
Company: Texas
Instruments
Timeline: 1977- 1979
Type: Scientific,
Programmable
Memory: 32 programming
steps, 10 memory registers
Power: AC adapter, 2
“AA” NiCd rechargeable batteries
Timeline
of the TI-55
The
original TI-55 was released in 1977 by Texas Instruments. It is the
most basic programmable calculator in Texas Instrument’s line
during the late 1970s, which the product line includes the TI-57
(Radio Shack EC-4000) and TI-58/58C/59.
The
TI-55 was later updated in the 1980s twice. The TI-55 II was
released in 1981. The good news of the update: memory increased to
56 steps, the sign, absolute value, fraction part, integer part
functions, and numerical integration were added. Bad news, a crummy,
unworkable keyboard! The keyboard was corrected with the TI-55 III
in 1986. Even though it would be unofficial, I would consider the
final version to be the TI-60 (no suffix) that would last from 1988
into the early 1990s.
Features
and Keyboard
*
Trigonometry
*
Hyperbolic Trigonometry
*
Logarithms, Anti-logarithms
* 8
sets of conversions: in/mm, gal/L, lb/kg,
°F/°C, degrees/grads, grads/radians, degrees-minutes-seconds
(DMS)/decimal degrees, polar/rectangular, all marked in blue
font.
*
Linear regression
*
Storage Arithmetic
*
Constant function for repeated calculation by pressing [ 2nd
] (Const). On later TI calculators, such as the TI-30Xa, this would
be labeled as K.
*
Simple programming up to 32 steps
The
[ 2nd ] (CA) (marked in
green): clears everything, including
programs and registers.
The
keyboard of the unit I bought is clean and all of the keys respond
well. Knock on wood it stays that way.
Storage
Arithmetic
The
TI-55 has 10 memory registers, registers are numbered 0 to 9.
Register arithmetic works as follows:
[
STO ] n: stores the number to register n
[
SUM ] n: adds the number to register n (STO+)
[
INV ] [ SUM ] n: subtracts the number from register n (STO-)
[
2nd ] (Prod) n: multiplies the number to register n
(STO×)
[
INV ] [ 2nd ] (Prod) n: divides the number by register n
(STO÷)
[
2nd ] (Exc) n: exchanges the number with the contents in
register n (x<>n)
Memory
registers 0 and 1 are free to use, but the rest of them can be
affected depending on what mode the calculator is in.
Conversions
There
are eight sets of conversions that are marked in light blue on the
calculator marked in this format: a ⋅ b
Pressing
[ 2nd ] before the key performs the conversion from a to b
(left to right, →).
Pressing
[ INV ] [ 2nd ] before the key performs the conversion
from b to a (right to left, ←).
Example:
[
2nd ] [ 4 ] (in ⋅ mm):
convert from inches (in) to millimeters (mm)
[
INV ] [ 2nd ] [ 4 ] (in ⋅ mm):
convert from millimeters (mm) to inches (in)
Polar-Rectangular
Conversions:
To
Rectangular: r [ x<>y ] θ [ 2nd ] (P
⋅ R): y [ x<>y ] x
To
Polar: x [ x<>y ] y [ INV ] [ 2nd ] (P
⋅ R): θ [ x<>y ] r
Statistics
and Linear Regression
In
single variable statistics, the y variable is used instead of the
customary x. The one-variable results are:
[
2nd ] (S. Dev): sy (sample deviation)
[
2nd ] (Mean): y-bar (arithmetic mean)
[
2nd ] (Var): σy^2 (population variance)
[
RCL ] [ 5 ]: Σy
[
RCL ] [ 6 ]: Σy^2
[
RCL ] [ 7 ]: n
For
linear regression (y = a * x + b), enter the x data point first,
press [ x<>y ], enter the y point, finally press [ Σ+ ]. The
[ 2nd ] (Σ-) is used to erase points. Since statistics
is accumulated in registers, we can enter as many points as we like.
[
2nd ] (Corr): correlation (r)
[
2nd ] (Slope): slope (a)
[
2nd ] (Intcp): y-intercept (b)
Predict
with x’ and y’.
The
TI-55 working primarily with the y variable carries over into linear
regression mode too:
[
2nd ] (S. Dev): sy (sample deviation)
[
INV ] [ 2nd ] (S. Dev): sx (sample deviation)
[
2nd ] (Mean): y-bar (arithmetic mean)
[ INV ] [ 2nd ] (Mean): x-bar (arithmetic mean)
[
2nd ] (Var): σy^2 (population variance)
[
INV ] [ 2nd ] (Var): σx^2 (population variance)
[
RCL ] [ 2 ]: Σx
[
RCL ] [ 3 ]: Σx^2
[
RCL ] [ 4 ]: Σxy
[
RCL ] [ 5 ]: Σy
[
RCL ] [ 6 ]: Σy^2
[
RCL ] [ 7 ]: n
The
TI-55 has a feature called automatic line trend entry. That is we
can enter data points as:
(n,
y1)
(n + 1, y2)
(n +
2, y3)
and
so on.
Start
with entering n [ x<>y ] y1 [ Σ+ ]. Then just enter the rest
of the y-data: y2 [ Σ+ ], y3 [ Σ+ ], and so on. The x values n +
1, n + 2, etc. are entered automatically. It sounds like a nice,
convenient, possibly underrated feature that is worth exploring. I
think this also works on the TI-57, TI-58/58C/59, and TI-66, but
please don’t quote me on it.
Keystroke
Programming
The
TI-55 has basic algebraic programming, which can hold up to 32 steps
(step numbers 00 to 31). The programming module is basic: no loops
as far as goto/labels, no prompts, and no comparisons (although some
tests can be used using backdoor methods such as 1/0).
There are only four commands:
[
2nd ] (R/S): Run-Stop
[
2nd ] (Rst): Reset, go to step 00 and continue execution.
[
2nd ] (Lrn): This sequence is the toggle between learn
(program) mode and calculator mode.
[
2nd ] (Sst): Single Step through the program.
The
TI-55 is in program mode when the display is in the format: SS RC.
SS:
step number
RC:
key code. R is the row number coming from the top down, C is the
column code is the column going left to right. The left most
column: C = 1 (unshifted), C = 6 (shifted). Right most column: C =
5 (unshifted), C = 0 (shifted).
There
are couple of exceptions:
Pressing
[ 2nd ] adds 5 to the column number. For example, [ % ]
has the code 22, while the [ 2nd ] (Δ%) sequence has the
code 27. The steps with the [ 2nd ] key are merged,
while the [ INV ] key (key code 21) is not.
Pressing
a number key gives RC in the format 0#. The [ 9 ] gives the key
code 09.
SS
represents the current step you are on. 05 00 means that you are on
step 5 and nothing has been entered. To review codes, we must use
Rst (reset) and Sst (single step).
A
sample program: f(x) = x^2 + 1.
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Hidden
Secrets
The
TI-55 has hidden key codes, which I have yet to explore, but here is
an article from rskey.org:
https://www.rskey.org/CMS/the-library/?view=article&id=98
Source
Woerner,
Joerg. “Texas Instruments TI-55” Datamath. December 5, 2001.
Retrieved November 11, 2024.
http://www.datamath.org/Sci/MAJESTIC/TI-55.htm
Manual:
http://www.datamath.net/Manuals/TI-55_US.pdf
To
those in the United States, Happy Veteran’s Day! Gratitude, take
care, and be safe,
Eddie
All
original content copyright, © 2011-2024.
Edward Shore. Unauthorized use and/or unauthorized distribution
for commercial purposes without express and written permission from
the author is strictly prohibited. This blog entry may be
distributed for noncommercial purposes, provided that full credit is
given to the author.
