The SR-51A is the next step after the short lived SR-51 calculator and it was the high-end calculator in the Texas Instrument line in 1975 together with the lower prices SR-16 and SR-50A. The SR-51A has the same functionality as the SR-51.
Vintage TI Articles
The Texas Instruments SR-50A calculator was intended to replace the SR-50 with a lower cost machine. Functionally, it does not add anything new, but it has an increased calculating precision when compared to the SR-50.
The SR-50 calculator was introduced soon after the HP-45 and it was the first TI calculator to have trigonometric as well as hyperbolic functions.
The Texas Instruments SR-16 is a scientific calculator but lacks the trigonometric functions. It was produced and sold for a relatively short period of time and it is less frequently seen than other models.
This red led vintage financial calculator is in fact not the first version of the Business Analyst released by TI; the first version had a black face and was released three years earlier. However they are functionally equivalent.
The Radio Shack EC-3001 printing calculator is a copy of the well-known TI-5050M portable printing calculator. It has 5 AA NiCd rechargeable batteries inside and used an AC9171 AC adapter. It uses thermal paper for printing.
New TI-59 magnetic cards used to record programs and data for the TI-59 calculators
Fully tested Texas Instruments AC adapter AC9130A. The adapter is used for a number of TI calculators among them SR-16, SR-50A, SR-51A, SR-52, SR-56, TI-2550 II, TI-2550 III (there are others too).