No doubt, all who have played with the Common Sense System have noticed that the weight on the ends of the longer, less-stiff rods, cause them to bend away from the horizontal before you ever add pennies.
Based on the premise that deflecting a rod 1/3 of the length would properly load it (for an average caster performing an average distance cast); I have been taking into account and including that distance (ie. amount of pre-load) in my measurements as part of the 1/3 deflection. In other words I start my measurement from where the rod would have been if not bent down.
It appears to me that up to a certain length and with very stiff rods, it doesn't make a valuable difference, but the longer and more flexable rods (like some fly rods) much more of a difference.
I'm hoping others here will share their thoughts on this and what they do.

The weight of the rod is part of the weight that loads the rod, therefore, you do not start your measurement from the tip, but from the horizontal butt per the instructions. From you wrote above, it sounds like you are doing this correctly.

If you take the measurement from the tip (point of droop) you will get an inaccurate reading.

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We agree with Tom and have done all of our CCS measurements without correcting for tip sag.

Jon

Thanks Tom & John... that's reassuring that I've been correct on that. Not sure what had put the doubts in my head.