Widely used computer-aided translation (CAT) tools divide documents into segments, such as sentences, and arrange
them side-by-side in a spreadsheet-like view. We present the first controlled evaluation of these design choices on translator
performance, measuring speed and accuracy in three experimental text-processing tasks. We find significant evidence that
sentence-by-sentence presentation enables faster text reproduction and within-sentence error identification compared to
unsegmented text, and that a top-and-bottom arrangement of source and target sentences enables faster text reproduction compared
to a side-by-side arrangement. For revision, on the other hand, we find that presenting unsegmented text results in the highest
accuracy and time efficiency. Our findings have direct implications for best practices in designing CAT tools.