Add trendline to timechart splunk

I am having the chart with durations, Now I want add a line over the chart with values as avg(duration). I used below query, but its not showing up trendline index=cloudfoundry sourcetype=cloudfoundry_apps "cf_foundation=px-npe01" "cf_org_name=Commissions" "cf_space_name=development" "cf_app_name=splunk** |search endDate !=null AND status='COMPLETED' |eval start_epoch=strptime(startDate,"%Y-%m-%d %H:%M:%S.%1N") |eval _time=start_epoch |eval end_epoch=strptime(endDate,"%Y-%m-%d %H:%M:%S.%1N") |eval duration=round((end_epoch-start_epoch)/3600) | chart values(duration) as duration by processLogId | trendline sma5(duration) as sma_Max_Resp My expectation will be as follows![alt text][1] [1]: /storage/temp/226640-chart-trendline.png