Yet another "almost programmable", the BA-55 is a business oriented calculator from Texas Instruments. Although obviously, business functions replaced common scientific functions such as trigonometric commands on this machine, it still unmistakably belongs to the same family as the TI-55-II or TI-55-III.

A remarkable oddity on this calculator is the presence of a printer port; this port connects to the same PC-200 printer as the high-end TI-66 programmable. (It'd be interesting to know if there were any other TI calculators with this proprietary serial port.) The calculator is even capable of listing programs, complete with alphabetic mnemonics! This is probably the lowest-end programmable calculator with such a program listing capability.

The programming model is very similar to that of the TI-55-II. No branches, loops, or conditionals, just sequential execution of a memorized series of keystrokes. The program area is too small for a Gamma function example, so here is Stirling's formula instead:

00 61    STO
01 01    1
02 85    +
03 01    1
04 02    2
05 54    1/x
06 55    ÷
07 71    RCL
08 01    1
09 50    ex
10 55    ÷
11 71    RCL
12 01    1
13 53    √
14 65    ×
15 02    2
16 93    .
17 05    5
18 00    0
19 06    6
20 06    6
21 95    =
22 91    EXC
23 01    1
24 60    yx
25 51    x-y
26 65    ×
27 71    RCL
28 01    1
29 95    =
30 13    R/S
31 37    RST