PSI - Issue 78

Galileo Tamasi et al. / Procedia Structural Integrity 78 (2026) 883–890

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Hewlett-Packard (HP) revolutionized calculator design by adopting Reverse Polish Notation (RPN), which streamlined input by eliminating parentheses and using a stack-based logic (Mier-Jedrzejowicz and Power, 2022; Mier-Jedrzejowicz and Wales, 2002). Early programmable workflows often involved drafting routines on paper to minimize input errors. Prior to pocket models, HP introduced the HP 9800 series - desktop calculators like the HP 9810A (1971) - capable of advanced structural computations, including matrix operations and equation solving. The HP-35 (1972) was the first pocket scientific calculator, followed by the HP-65 (1974), the first programmable model with 100 steps, 9 registers, and magnetic card support. The HP-67 (1976) extended these capabilities to 224 steps and 26 registers, becoming a key tool in engineering practice. Its desktop counterpart, the HP-97 (1977), added a thermal printer for traceable output. The HP-41C (1979) marked a major leap with alphanumeric display, expandable architecture, integrated clock, and peripheral support, establishing itself as a long-standing standard in professional environments. Texas Instruments (TI) adopted algebraic notation (AOS), offering a user-friendly alternative to RPN. The SR-50 (1974) marked TI’s entry into scientific calculators, followed by the programmable SR -52 (1975) with 224 steps, 20 registers, and a magnetic card reader (see Fig.4). The TI-58 (1977) introduced "Solid State Software" via ROM modules, expanding capabilities to 480 steps and up to 60 registers, and allowed printing via the PC-100A. The TI-59 (1977), TI’s flagship, offered 960 steps, 100 registers, ROM expansion, and ca rd/printer support. Olivetti, meanwhile, focused on office-oriented desktop programmables after the Programma 101. Key models included the Logos 68 (1971), Logos 75 series (1975), and Logos 80B (1978), emphasizing memory and speed. The P6040 (1975) integrated display, printer, and minidisk storage, bridging calculators and early computing.

Fig. 4. Texas Instruments calculators timeline.

By the late 1970s, programmable calculators had significantly advanced in memory, speed, and integration. HP distinguished itself through RPN logic and build quality, TI through algebraic entry and affordability. These tools transformed engineering workflows by automating complex calculations and enhancing productivity. 6. Simulated design Simulated design is a methodology that recreates the decision-making and computational processes of a past era, using the tools, knowledge, and constraints of that time (Ozsarac et al., 2025). For 1970s bridge seismic analysis, this means faithfully reproducing the design environment. The process involves historical research to gather period regulations, manuals, and calculator guides, alongside studying real projects (Crisci et al., 2022). Next, calculation models reflecting 1970s methods are identified and translated into algorithms optimized for programmable calculators like the HP67/97. These algorithms are then implemented and validated on emulators or original hardware, often using pre-programmed magnetic cards. Beyond user-developed solutions, Hewlett-Packard provided significant application software, notably the five-volume HP67/97 Ingegneria Civile series by HP Italia and university faculty (HP Italia, 1980, 1979, 1978, 1977a, 1977b). Analyses apply these algorithms to case studies using 1970s loads and seismic criteria for stress, dimensioning, and reinforcement checks. Results are compared to modern analyses (e.g., FEM) to