There are several measurements that need to be made prior to doing a delay measurement. You need to measure the height of the pedestal before the front porch. Use a MEASURE High, with histogram determination of the high.  Gate the measurement with cursors on the bar. Measure the blanking level, using same procedure, but with cursors on the blanking area. Measure the negative sync pulse amplitude, using same procedure and gating inn the sync area. Subtract the measurement made in step 2 from the measurement made in step 1.  Divide by 2 and write down this value. The measurement made in step 3 from the measurement made in step 2. Divide by 2 and write down this value. Go to the measurement setup.  Select Delay measurement Select reference LEVELS SETUP Set units to absolute Set mid ref source 1 to the value determined in step 3 Set mid ref source 2 to the value determined in step 4. Delay measurement is now set up correctly for the signal.