Detecting errors in command and specification words When a command is activated and it does not correspond to any known Survo operation, an error message is displayed. If the command word is close enough to some real Survo commands, the error message includes a list of possible alternatives thus guiding the user to detect a typo etc. The alternative commands are found by computing the Levenshtein (edit) distance d between the given command and each possible real command and listing the command words having the shortest distance. The list of alternatives is shown when d<3 and there are less than 6 words in the list. In Survo, Levenshtein distance is slightly modified by permitting inter- change of two consecutive letters in the edit operations (see STRDIST?). Specification words: By default, specification words are not checked. Checking them is turned on by the command SYSTEM spec_check=1 (or by the soft buttons SYSTEM -> SPEC). When a Survo operation is activated and checking is on, all pertinent specification words (like HOME in HOME=200,300) are compared to a list of all specification words usable in that operation. If a specification word does not correspond to any allowed word and Levenshtein distance to the closest one is less than 3 and there are not more than 5 such words, an error message (containing a list of alternative words) is displayed and the operation is interrupted. Since the user may have his/her own specifications which are not relevant in the current operation but resemble some actual specifications, this procedure may sometimes lead to false alarms. Therefore it is advisable to turn spec_check on only after encountering difficulties in activation. Checking may then discover typos etc.