sjthomas@cup.portal.com (Stephen J Thomas) (09/07/90)
The next article in this collection is a rather lengthy review of the TI-81 Scientific Graphics Calculator. This warning is provided so you can bypass 12.6K of text if you are not interested. Stephen J Thomas sjthomas@cup.portal.com sun!portal!cup.portal.com!sjthomas
sjthomas@cup.portal.com (Stephen J Thomas) (09/07/90)
TI-81 ADVANCED SCIENTIFIC GRAPHICS CALCULATOR REVIEW
The TI-81 is Texas Instrument's recent entry into the graphical
calculator field. TI's current calculator marketing emphasis is to
the educational sector -- mostly elementary and high school, with the
TI-81 designed especially for the latter. In fact, the 81 has not
been released into the general market place (don't look for it at
Walmart!), but is available only through TI's school suppliers and
school book stores. Individual units can be purchased by educators
directly from TI at the list price of $110. Both EduCALC and Elek-Tek
are TI school suppliers, and will sell individual units to anybody at
their discounted price of about $90.
I've had the opportunity to experiment with a TI-81 for a little
while. The following review attempts to consider the 81 on its own
merits and not to compare it TOO MUCH :-) to the HP-48SX. I've
never used a Casio graphics calculator, but have been told the 81 is
comparable to the Casios.
_SPECS_
The display is gray-colored (like the HP-28), 96 pixels wide and
64 high, supporting 8 lines x 16 characters. There is one character
size, with several special characters such as a superscripted 2 when
entering n-squared. There are no annunciators "outside" the pixel
display, but a 4x4-pixel square appears in the upper right corner of
the display as a "busy" indicator. Alpha mode is indicated by the
letter 'A' inside the cursor; [shift], called [2nd], by an up-arrow.
The 81 is shipped with 4 AAA batteries and an owner's manual. No
quick-reference guide is included, although they are found with many
simpler TI calculators. The case is a hard plastic cover which slides
off the front of the calculator, and can be slid onto the back for
storage while in use.
The casing is a deep blue plastic. Most keys are approximately
11x5.5mm -- black, blue, light blue, and gray, with white lettering.
Shifted functions are in light-blue above the key to the left, and
alpha characters are in gray above the key to the right. There are
rubber feet on both the calculator back and the protective case.
There are 27 global variables which may each contain one real
number, over 30 dedicated variables (for statistics, display
parameters, etc.) and 3 matrices up to 6x6 each. In addition, 2400
bytes of RAM are available for user programs and statistics lists.
Other than using the single-letter variable names in algebraic
computations or expressions to be graphed, symbolic math is not
supported. By limiting the user variable names to one character,
implied multiplication is often allowed. Variables can be used
virtually anyplace a numeric value can. If no value is stored in a
variable, zero is supplied as the default.
The logic is, of course, algebraic -- but some aspects are
different than previous TI calculators I have used (TI-35, 59). For
instance, to calculate sin 30, you MUST press the SIN key first ("sin"
appears in the display), followed by the argument. [ENTER] completes
the computation line and displays the result. Similar syntax is
required for other functions, such as e^x, log, etc. Both the result
of the previous computation and the expression itself are stored and
can be recalled for use in the next computation line. Surprisingly,
there is no [=] key; [ENTER] is used instead. Function names can not
be entered by spelling them out with the alpha keyboard. For example,
typing in [alpha-lock] SIN is interpreted as S*I*N, not the sine
function. All variables are global -- shared by all programs and
applications. The variables X, Y, T, R and theta are used and altered
by graphing routines.
_MODES_
Pressing the [MODE] key displays a menu to set the various modes
of the calculator: display, radian/degree, polar/rectangular,
function/parameter plots, un-/connected plots, etc. To check the
current state of the calculator settings, you must check the [MODE]
menu -- highlighted items indicate current modes.
_MATH_
19 math functions are on the keyboard (shifted and unshifted).
Pressing [MATH] displays the first of four "pull-down" menus of math
functions: general, NUM (like MATH PARTS), hyperbolics and probability
-- providing 21 more functions. The cursor is moved to the desired
menu heading with the left- and right-cursor keys; then the
appropriate choice is made by either selecting the number of the
desired function, or highlighting it with the up- or down-cursor keys
and pressing [ENTER]. The [TEST] menu provides the six standard
in/equality relational operators (=, >, <, ...) which are used to
determine a truth value (0 or 1) for program branching and keyboard
comparisons.
_STATISTICS_
Statistic functions are list-based, and include 1-variable,
linear, logarithmic, exponential and power models. Histograms and
scatter plots can be generated.
_PROGRAMS_
Up to 37 programs can be created. There are GOTOs and LBLs, IS>
and DS< looping and a Do-If-True test structure (IF). Most of the
capabilities of the machine are programmable. Program steps are not
numbered. Programs can call other programs as subroutines (maximum
of 10 levels).
Statistics lists and programs comprise a maximum of 2400 bytes.
_MATRICES_
Matrix capabilities provide for four matrices (called [A], [B]
and [C] -- with the brackets -- plus one temporary matrix for
intermediate results) which may each be up to 6x6. Entering or
editing a matrix is done by either using subscripts or via an edit/
entry screen. A nice feature in the entry/edit screen is a pixel
representation indicating which element the user is editing. For
instance, for a 4x5 array, a 4x5-pixel block is displayed with the
pixel corresponding to the current element remaining clear (off).
This is useful to whose of us (well, for me anyway) who confuse
element (2,4) with element (4,2). This is what is shown for element
(2,4) of a 4x5 matrix (sorry if the spacing is disrupted by the mail
system):
XXXXX
XXX X
XXXXX
XXXXX
Standard matrix functions (+, -, invert, determinant, scalar *, etc)
are provided, along with the ability to swap, add, and multiply rows
(but apparently not columns). Since no type of matrix division is
defined, solving a system of equations is not as easy as on the HP28
or 48.
_GRAPHING_
Up to four equations in the form y=f(x), or four sets of
parametric equations in the form x=g(t), y=h(t) can be graphed at one
time (simultaneously or sequentially). The [X|T] key types X when in
function mode and T in parametric mode as a typing aid (don't have to
press [ALPHA] first). Polar plotting is also supported. Similar to
the 48SX, the user can specify the x & y minimums & maximums, scale
and resolution.
ZOOM features include BOX, IN, and OUT. The ZOOM IN/OUT
parameter must be specified before the function is executed -- these
factors are used until changed by the user or reset to default (4x or
0.25x). The SQUARE function adjusts the scale so that the graph of a
circle looks round. To ZOOM BOX, you exit the graph display, select
BOX from the [ZOOM] menu, and are returned to the graph display. Set
one corner of the box by pressing [ENTER], then move to the other
corner. As you move the cursor to the opposite corner, a dynamic box
is very quickly drawn corresponding to the current cursor position --
so you can easily see the box to be ZOOMed. Pressing [ENTER] a second
time plots the ZOOM BOX.
With any graph display, the cursor can be moved around and the x-
and y-coordinates are shown at the bottom of the screen. An
interesting TRACE mode 'locks' the cursor to the (first, if more than
one) equation plot. Using the left- and right-cursor keys moves the
cursor along the function plot, showing the x and f(x) coordinates at
the bottom of the screen. The up- and down-cursor keys move the TRACE
cursor to other functions plotted in the current graph display. If
you move the TRACE cursor to either the left or right extreme of the
plotted function and try to move past the edge, the entire graph
shifts over about 8 or 10 pixels, and more of the function/s is/are
plotted. [This should be in the 48SX!] The manual states that TRACE
mode allows the user to 'explore the function graphs.'
Five dedicated keys immediately below the display (which look
like menu keys to HP users) provide the following functions: [Y= ]
(area to list equations to be plotted), [RANGE], [ZOOM], [TRACE], and
[GRAPH]. The operating system keeps tabs if any graph-related
parameters have changed since the last plot. If so, the graph is
redrawn by [GRAPH] or [TRACE]; otherwise, the previous graph is just
redisplayed. The [DRAW] menu provides functions to clear the graph
display, draw lines (fun because the line is displayed as you move the
cursor around after you set one endpoint, similar to ZOOM BOX), set,
clear or invert pixels, and to shade regions (with variable
resolution/intensity) between two functions.
Initially, the TI-81 appears to plot much faster than the
HP-48SX. However, the 48 plots 131 points per function while the 81
plots only 96 (at maximum resolution). Also, the 48 takes about one
second after executing DRAW to clear the screen and draw the axes
before plotting begins. On the 81, this initial set-up is virtually
instantaneous, and plotting begins immediately. If you eliminate
these two factors, the actual point-by-point plotting speeds are
almost identical on the two machines -- with perhaps a slight
advantage going to the 81 in most circumstances.
_WHAT'S MISSING_
1. Most significantly, a SOLVER. After enjoying HP-SOLVE or several
years, I can not imagine using a calculator without it. [Does HP
have it patented?] The 81 manual states that you can determine
roots and intersections of functions graphically, by controlling
the resolution and using TRACE mode -- and you can, but it is
clumsy compared to the SOLVER, and requires a large ZOOM IN factor
for significant accuracy. It also doesn't provide the 'solve-for-
any-variable' capability.
2. Complex numbers
3. Back-arrow correction key. Have to use [cursor-left] [DEL] is
cumbersome.
4. Spiral binding in the manual. Trying to use the manual and the
calculator simultaneously is very frustrating.
5. Examples in the manual -- there are far too few. Several
application programs are provided as examples.
6. Annunciators outside the pixel display.
7. Tactile feedback from the keys. They have better spring-back than
some earlier TI calculators, but not as good as HP [where it has
seriously degraded in all machines after the HP-41, especially the
left-shift key on my 48!]
8. Diagnostic self-tests.
9. Verbose error descriptions. On meeting an error the 81 displays:
ERROR nn $$$$$$ and gives you the option to abort or goto the
source of the error condition. nn is an error number up to 19,
and $$$$$$ is a one word indication of the error, such as MATH,
MEMORY, SYNTAX. Several numbers may have the same error-word.
10. A beeper.
_SUMMARY_
Overall, the TI-81 is a reasonable choice for high school
students [who are allergic to RPN :-) ]. I would have appreciated
being able to generate graphs quickly in trig or calculus class. The
price (less than US$90 through the mail) is not out of range for many
students (or more correctly, their parents). TI is making an overhead
projection unit available (at $279 list -- or free if you purchase 90
TI-81s!) -- and is hoping the unit will become a standard in many
schools. There is no real comparison between the HP-48SX and the
TI-81 -- they are in different leagues. Perhaps somebody will provide
a comparison of the 81 with the Casio graphic calculators. At least
the 81 has larger keys!
Thanks: Thanks to the TI employee (whose name I don't recall) who
would not lend me a TI-81, but was very helpful with information.
Cowardly disclaimer: Any opinions expressed are mine, and also of all
right-thinking individuals. Most of the information is from using the
TI-81 for about one week; some details may be inaccurate (I hope
not!) or not presented in the required depth.
Directions: Stephen J Thomas
sjthomas@cup.portal.com sun!portal!cup.portal.com!sjthomas
P.O. Box 371861, El Paso, Texas 79937-1861pedz@bigben.mpd.tandem.com (Perry Smith) (09/08/90)
>7. Tactile feedback from the keys. They have better spring-back than > some earlier TI calculators, but not as good as HP [where it has > seriously degraded in all machines after the HP-41, especially the > left-shift key on my 48!] Agreed!!! I think the 48SX is better than my old 28C. The 28C was so bad that I had to watch what I did and could not just trust my fingers. Thats really bad I think. pedz