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.
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 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 Commodore SR4148R scientific calculator has been refurbished and its battery has been changed. The calculator works perfectly.
The Wang 450 desktop calculator is one of the last large calculators made by Wang. The 400 family was the last series of calculators made by Wang and the 450 Scientific is one of the series.