|"Texas Instruments" and "rare"
sounds like a contradiction. Anyone who searches for early electronic calculators quickly
senses the extent to which TI dominated the market in the 1970s. A count through my own
collection revealed over 40 different models and there are many I don't have! It would be
easy to conclude that all TI calculators are commonly found and not much of a challenge to
the avid collector.
However, this is not the case. There are many rare models and a few less-common variations
of well-known models. TI had a tendency to replace their calculators quickly with improved
or lower-priced versions, particularly during the price wars of the mid-70s. They also had
such extensive product lines at times that their own products must have competed against
For this article, I divided TI calculators into four categories based on degree of rarity.
The judgments are based on my experience searching through flea markets, garage sales,
thrift shops, and collector lists (and encountering thousands of calculators in the
process), on numerous conversations I have had with other collectors, and on some library
research. The year of introduction is noted in parentheses following the model number.
30 (1976): You probably
know this one. No doubt the best-selling calculator ever.
55 (1977): Budget scientific model.
59 (1977): Surprisingly common, given its expense and
sophistication. Sometimes found with the PC-100 printer.
1025 (1977): Often found in the original box.
1200 (1975): Also often found in the original box. The 1200 series styling was used on
many other TI calculators and they all shared the annoying characteristic of loose or
1750 (1977): TI's 1st LCD calculator.
Business Analyst - I (1979)
Little Professor - 2 versions (1976, 1978): On the early version, the on/off and level
switches are on the side; on the later version, they're on the front.
58C (1979): Model 58 with continuous memory.
1270 (1976): Colorful model. TI appeared to like orange.
2500 Datamath - 2nd version (1973): There are two
versions. The first earned a "best buy" from Consumer Reports; the second earned
a retraction from Consumer Reports five months later. How can you tell the difference? The
earlier has a recharging time of 16 hrs. (stated on the back of the calculator); the
second recharges in 10 hrs. Apparently there are also differences in the display angle and
brightness (which resulted in Consumer Reports' action).
2500 - II (1974): Similar to 2500 but has % key and cheap logo strip that tends to peel
off. Eventually sold at give-away prices.
SR-10 - 2nd version (1973): Again, two versions. In the
first version, the "SR-10" logo is situated in the escutcheon surrounding the
display. In the 2nd version, the logo moves down to the upper area of the faceplate. All
advertising photos, manuals, and boxes I've seen show the 1st version, though it's far
Business Analyst (1976): The first in a long line of popular financial calculators.
58 (1977): Replaced with the 58C in 1979.
1050 (1977): Another entry in the 1000/1025 line, but not nearly as plentiful.
1265 (1976): Has a blue fluorescent display, unique within the 1200 series.
1400 (1976): Has a brown carrying case, not the usual black. Similar styling to the 1200,
but a little higher quality.
1500 (1974): Nifty little unit with thick chrome borders - one of my favorites.
1600 (1976): The 1600 series consisted of slimmed-down models that prefigured the styling
of LCD units. They are surprisingly difficult to find.
1680 (1977): This one could re-display previous entries and allowed some primitive editing
of those entries.
2500 Datamath - 1st version (1972): TI's first pocket calculator.
2550 - II (1975)
2550 - III (1976)
5050M (1976): Handheld printing unit with memory.
DataMan (1977): Very unusual child's calculator that looks like a robot.
Money Manager (1977)
SR-10 - 1st version (1972): TI's first "SR"
(Slide Rule) model.
SR-16 - II (1975)
Difficult or Very Difficult:
76 - "Spirit of 76" (1976): Red/white/blue
Bicentennial (of the USA) model. Another 1200 progeny.
150 (1974): Possibly the rarest TI. The keys and body style of 2550, painted-on silver
trim of SR-10. No memory or fixed decimal switch as on 2550. Unusual orange display.
1200 "Lady" (1975?): The 1200 with more "feminine"-colored faceplate
1205 (1976): Another colorful 1200 relation, but this one has oversized lettering too.
1220 (1976): This (and the 1225) are somewhat obscure, but otherwise ordinary, 1200 series
2510 (1973): Similar to 2500, but chronologically sandwiched somewhere between the
2500 and 2500 - II, probably failing to land a market niche in TI's crowded product line.
Calculator body is a lighter cream shade compared to 2500's beige. Uses disposable
5050 (1975): I believe this was the 1st handheld printing calculator with vertical
DataClip (1977): LCD calculator shaped like a 6-inch ruler. High-quality, unlike its many
SR-16 (1974): Superseded by the SR-16II within a year. This model is borderline
SR-51 (1975): TI replaced the SR-50 and SR-51 in mid-1975 with the "A" models.
The SR-51 had been marketed only a few months when this happened, so it's quite rare. This
calculator is also more stylish than any of TI's other advanced models. Another one of my
Wiz-A-Tron (1976?): Child's calculator similar to Little Professor but with wizard rather
than owl on face. Very colorful.
TI made calculators for sale under other names, including Radio Shack. These are more
difficult to locate than the TI versions. Some examples are (1) the Longines Symphonette
2500, a clone of the TI 2500 Datamath (2nd version), but in a green color, (2) the Exactra
line (models 19, 20, 21, 22, and 23), reminiscent of the more colorful 1200 models, but
sold as early as 1973, and (3) many Montgomery Ward models (identified by the
"TXI-" prefix to the model number). The Montgomery Ward calculators are
especially fascinating as they are not obvious clones yet can be identified as related to
specific TI models.
Some models are difficult to find in good condition. The SR-10 and 11 are notorious; the
silver trim is almost always worn on these models. An SR-10 in near mint condition would
definitely qualify as "Difficult". The SR-50, 51, and 52 suffered from paint
wear around the switches and later TI models often have loose nameplates and missing
battery covers. Other models, such as the 2500 and 2550, are usually in quite nice
condition. Most models are rarely found with the original box and paperwork; out of dozens
of TI 30s that I have seen, only 1 or 2 have been new-in-box. Interestingly, some of the
earlier models, such as the SR-10 and SR-50, appear to be easier to find with the box,
although the boxes tend to show wear easily.
Since my article first was printed, I have
discovered/been informed of additional models, which all appear to be somewhat rare. These
Concept 1 and 2: same style as 1200 series but with a two-tone rust and gray faceplate.
SR-22 (1973): desktop-sized model with programming functions such as hexadecimal and octal
2500 Datamath (LCD version): Prototypes were produced, but display unreliability prevented
it from being offered to the public.
45: scientific model with a fluorescent display; similar in styling to the TI 30.
Longines-Symphonette Electronic Calculator (1972): Last issue, I mentioned a
Longines-Symphonette similar to the TI 2500B. I have since discovered one similar to the
early version of the 2500. This one has a serial number of only 3201 and the (TI) charger
has a date stamp of July 1972, just one month after TI started production of the 2500,
indicating that TI was manufacturing these clones right from the start. It has the same
green case color as the other.
Finally, TI calculators often have a data code stamped on the back. It appears to consist
of a two-digit week and two-digit year, such as "4376", for the 43rd week of
1976. TI chargers, too, have date codes, expressed as month and year, such as "7