When speech input is the only form of input available, alternatives forms for critical entries should be allowed, so that if the system cannot recognize an entry after repeated attempts, another entry form can be substituted.
Additional Information:
Because speech recognition systems are affected by normal variations in a user's voice, and by changes in the acoustic environment, a spoken entry that was accepted yesterday might not be accepted today. Thus, for important entries a user should be able to use an alternative word. For example, "Exit" might be defined as an acceptable substitute for "Finished." Spelling a word letter-by- letter is not an acceptable alternative, since speech recognition systems may have trouble correctly identifying similar sounding letters.