This paper will review selected speech intelligibility indicators including word scores. %AL[inf cons], and speech transmission index. The implied relationship between indicators will also be deduced based on work and experiments by others. These relationships will be presented on a new scale known as the ``Common Intelligibility Scale,'' which is currently under consideration for incorporation into measurement standards in the United Kingdom. Finally, the use and applicability of various indicators will be discussed, including sensitivity, ease of prediction, and measurement.