need help finding the Write cahce hit ratio chart in analyzer nar file

I have a nar file and I am trying desparately to find the chart showing the % dirty pages (known as Write Cahe Hit Ratio)... when I select a lun and hit the peroframcne detail... the options I have to chose are Utilization, Queue length, Response Time, Ttl Bandwidth, Ttl Throughput, Read Bandwitdh, Read Throughput, Read size, Write Bandwidth, Write size, Write Throughput and service time. Does anyone know what I am doing wrong? Where can I find this option, thanks for any suggestions.