Prior to Field Day I was plotting a  SWR curve to determine my 2:1 bandwidth  on my half wave tuner and ran into a problem. I only use a single coil without taps and a single capacitor combination on my minimum parts half wave tuner and wanted to find the bandwidth on 40 meters after I had tuned for minimum output/SWR. But I found that the SWR curve was badly skewed on 40 meters when my variable was  tuned to around 15-20 pf.  Can you spot what caused this problem?  I fiddled with it for quite a while -  more time than I care to admit. 
Z