Many people make a living by selling antique and collectible science instruments, which these days include early electronic calculators. Unfortunately, a lot of these calculators are in a sad shape after years of abuse or neglect. Often though, the units are not quite dead yet; at least not until a well-intentioned, but inexperienced dealer makes an attempt to test them, and causes irreversible damage.

Here are a few words of advice if you're selling calculators that you're not familiar with:

• ALWAYS remove rechargeable batteries from the calculator if they can be removed without disassembly (you need the batteries when testing the unit, but not when it's shipped or put in storage.) Old Nickel-Cadmium batteries often release corrosive gases (the electrolyte KOH, or potassium hydroxide, a strong base) that can permanently damage the insides of the calculator. It's quite likely that the calculator is already damaged, but you can at least somewhat reduce additional damage by not leaving the dead battery pack inside the calculator.
• NEVER throw old rechargeable battery packs away, no matter how yucky they look. The NiCd cells themselves may not be worth anything, but often, the plastic casing is irreplaceable. Experienced collectors can easily rebuild the pack by cleaning the plastic, removing the dead cells, and replacing them with new NiCd cells. Always ship dead battery packs with the calculators if possible, just don't leave them in the calculator!
• NEVER test a calculator using anything other than its original charger, unless you know precisely that the charger you're using is compatible. Overvoltage, undervoltage, reverse polarity, using a AC charger with a DC calculator or vice versa, can permanently damage the calculator in a split second. Particularly vulnerable are "continuous" or "constant" memory models in which a highly sensitive memory circuit is connected directly to the power source, with no protective components in between.
• NEVER test a calculator with a charger when there are no batteries installed, unless the manual explicitly states that the calculator can be operated this way. In many calculators, the internal rechargeable batteries also double as voltage stabilizers/regulators; when you use a charger with no batteries present, the calculator may receive excessive or unregulated voltage and permanent damage may occur in seconds. Do not assume that you're causing no damage when you see that the calculator works and responds to keystrokes. You may not even notice that there's a problem, until your buyer complains that the calculator does not operate reliably, makes arithmetic errors, or has trouble storing and recalling numbers in registers or program steps. These types of problems are often the result of operating the calculator from a wall charger but with no batteries inside.
• ALWAYS make sure that you leave the calculator's switch in the OFF position. Even when the internal batteries appear discharged, there may be some current left in them; discharging them further can aggravate the outgassing problem and can also permanently kill rechargeable batteries that might otherwise be salvageable.
• NEVER substitute alkaline batteries for Nickel-Cadmium cells, unless the manual explicitly states that the calculator can be used with such batteries. The voltage of NiCd cells is approximately 1.3 Volts when fully charged, whereas a new alkaline battery gives out almost 1.6 Volts. When three cells are connected in series, the difference can be nearly 1V, which is enough in some cases to permanently damage the calculator's electronics.
• NEVER try to fix a calculator's magnetic card reader by repeatedly pushing cards through or pushing through an abrasive cleaning card. That black yucky stuff that is deposited on the cards isn't dirt; it is the disintegrating rubber pinch wheel inside the card reader. The more you try to test the reader, the more of this yucky stuff gets deposited all over inside, making it that much harder to repair the unit. Moreover, as the wheel gets increasingly stuck in this gummy deposit, further tries can actually damage the motor or the little clutch that protects the motor from overload, turning an otherwise routine repair job into a difficult or impossible one.

This is not just fiction, by the way; I've seen several calculators recently that were damaged one way or another by persons who didn't know any better and were trying to be helpful. If you're a dealer or seller of vintage calculators, please keep your customers happy by not destroying or severely damaging a beautiful, but fragile, old electronic instrument. I, for one, will be grateful when I buy something from you.

A Note about TI-59 Calculators and "Magnetic" Cards

Many TI-59 calculators come with a little booklet containing factory-labeled plastic cards. Most of the time, these are not magnetic cards, and should not be fed in the calculator's card reader. These cards are merely plastic label cards that come with solid state library modules, and are meant to be inserted into the slot under the calculator's display, just above the A...E keys.

You can tell the difference between these label cards and real magnetic cards as follows: the edges of a real magnetic card are always perfectly smooth (label cards may have bumps where the card was separated from a plastic sheet); the back side of a magnetic card is also very smooth, with a matte appearance, like the tape in an audio cassette (label cards usually have a shiny plastic surface on the underside.)