Twenty students having a comparable typing skill and speed (about 150 strokes per min) performed series of typewritings with contents well familiar to them. These writings were examined for errors (error = deviation from a given program of stroke sequences). The errors could not be caused by ingnorance of writing or spelling of the words. Two categories of errors ("exchanges" = "Verwechslungen" and "omissions" = "Auslassungen") were explained to result from special "faults" in the data

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... g controlling the typing process (Fig. 3). The occurrence of these types of errors dependend on interactions of the following factors: 1. Preferences of succession which (in general) related the first letter of an actual letter-combination with the second one (also) in contrary succession (i ⇄ e) or with other letters, not occurring in the combination (n → d ; n → g) (Tab. I ) . 2. Tendencies of the particular letters of an actual sequence of letters ( = word) to occur already before and/or after the right sequential position (sequential interval of this effect ≤ 4 strokes; temporat interval: about 1 sec; Figs 1, 2). 3. Correspondences in particular characteristics of special letters (vowel-vowel-exchange, etc.). 4. The notice to type as quickly as possible. Interactions of these factors resulted in erroneous "anticipations" and "postpositions" of letters.