The C series Clarity measures are used widely outside the United States, especially in Europe.

C7 is equivalent to the D/R ratio widely used in the United States and represents another way to look at the strength of the direct sound field. It displays the ratio of direct to reverberant sound in dB using a Split Time of 7 ms. Split Time refers to the point at which early reflections are no longer considered beneficial and become a part of the reverberant sound field. In general, values above -15 dB show good localization (a good D/R Ratio). The closer the value comes to 0, the better the localization.

C50 is used to project speech intelligibility and is similar to Alcons with a 50 ms Split Time. It displays in dB the ratio of energy before and after 50 ms. In general terms, any value above 0 dB represents good intelligibility in a room with normal reverberation. In rooms with higher than normal reverberation any value above 5 dB is generally considered good.

C80 uses an 80 ms Split Time to predict the articulation (clarity) of different types of music. In other words it provides insight into the musical performance of the room. The C80 map shown above indicates this room is going to perform better on music than it does on speech.
Csplit allows you to look at the effect of different Split Time settings by allowing you to set the Split Time.