Here's how you measure the tongue weight.
FIRST: Move stuff out of the way. (Sorry, cheap shot to show my Vette.)
Then you can take the weight off the tongue in two ways - 1. Attach it to your towing vehicle, or 2. Put the tongue on a set of wooden blocks (as I did).
Slide the scale under the jack tube.
Now jack the load UP so that the blocks are free and the entire tongue weight is on the scale.
As you can see, my UNLOADED trailer has a tongue weight of about 750 lbs.
Now the SECOND place to check your tongue weight is actually under the hitch coupler. Again use wooden blocks to place the scale in position. Use the jack to raise the tongue.
Once the scale is in place, lower the jack so that the trailer is balanced on the scale.
And you can see that my "true" tongue weight at this location is about 725 lbs - just slightly less than at the jack location. At the coupler, you'll get a more accurate reading of the "true" tongue weight, but as you can see the difference is not worth the extra effort.HERE'S MY NORMAL ROUTINE:
Once my trailer is loaded, I back the truck to it and attach the trailer.
Then I raise the jack so that I can get the scale under it.
Next I put the scale under it and jack up the tongue until it's off the truck's ball.
Looking at the scale, I have a great idea of what my tongue weight is.
Again, you can see that the slight difference between the measured weight at the jack and the coupler is not worth the extra effort (when you're already hooked up to the vehicle).
And this is a quick and simple way to measure your buddies rig. Don't remove the chains or electrical connection, but DO release the load-leveler links.