## 5 Discussion  
SHERPA analysis shows that brackets and cushioned loop clamps are particularly sensitive to operation in the wrong direction (A3) and to misalignment (A5). These error modes can be considered geometry-related since the proper installation of these parts requires some spatial abilities. Information errors such as the acquisition of the wrong information (R2) and incomplete information retrieval (R3), also identified during SHERPA analysis, can be considered precursors to geometry-related errors because of the impact of the information system on the assembler's cognitive load [25]. Simultaneously, HEART results show that brackets and cushioned loop clamps had the highest human error probabilities (0.62 and 0.47 respectively) compared to fasteners (0.29) and cap covers (0.09). Interestingly, the lack of a means of conveying spatial and functional information to operators in a form that they can readily assimilate is a major error producing condition (EPC) in the HEP calculation. This EPC was the single most important in the HEART analysis (\(\times\)8 multiplier) and represented 49% and 42% of the total contribution to human error probabilities for brackets and cushioned loop clamps respectively. The results obtained by using HEART were consistent with results from an empirical study in truck engine assembly where the potential error reduction obtained as a consequence of changing the information system was in the order of 40% [28]. It is important to highlight that the work instructions were provided as text and 2D drawing sheets on a stationary PC display, which has been found to be less effective than 3D instructions when spatial abilities are required [87]. It has been acknowledged that work instructions are often deficient or underused in final assembly [25,26]. Another point of concern is how the assembler interacts with the work instructions. The computer screen displaying the instructions in the study case is located on the workbench. However, the worker is frequently at some distance from the screen during the actual assembly. Instructions may not be easily readable from a distance, nor may the worker be able to figure out details on the drawings. This will demand frequent trips from the assembly position to the workbench to retrieve information. Larger screens could help, although the worker's movement around the assembly position might still frequently leave the screens out of sight. This situation was reported by [PERSON] et al. [35]: a large overhead screen was installed on an aircraft part assembly line, but the worker had to move to retrieve \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**EPCs** & **Maximum Multiplier** & **Brackets** & **Cushioned Loop Clamps:** & **Fasteners (Bolts-Nuts)** & **Cap-Covers** \\ \hline (5) No means of conveying spatial & & & & & \\ and functional information to & & & & & \\ operators in a form which they can & & & & & \\ readily assimilate & & & & & \\ \hline (12) A mismatch between perceived & & & & & \\ and real risk & & & & & \\ \hline (13) Poor, ambiguous or ill-matched & & & & & \\ system feedback & & & & & \\ \hline (17) Little or no independent & & & & & \\ checking or testing of output & & & & & \\ \hline (26) No obvious way to keep track & & & & & \\ of progress during an activity & & & & & \\ \hline (31) Low workforce moral & & & & & \\ \hline (39) Distraction and & & & & & \\ task interruptions & & & & & \\ \hline _Human Error Probability_ & & & & & \\ \hline \hline \end{tabular} \({}^{1}\) Symbol - indicates that the corresponding EPC (row) was not identified during the analysis of the part under consideration (column).  
\end{table} 
Table 5: Consolidated results of HEP calculations and error producing conditions with their respective % contribution \({}^{1}\). the information because the screen was not visible from all angles and working positions. Neither do wide screens solve the need to move to the workbench to interact with the work instructions (validate, close instructions, go to following instruction, etc.