I just weighed my NX-250 and TX-150 and got some interesting results. I'm getting ready for a hike and making a database of the weight of all my equipment. I used a digital postal scale and out of all my gear, only a few items varied from their listed weights. One was my Granite Gear Wisp pack that weighed 3oz more than listed. Another thing were a few Mountain House meals that were about an ounce more then listed.
Here is the big deal though:
NX-250 (listed as 3lb 10oz on Clark site) Mine has a pair of 12ft whoopie slings and two 38g biners packed together and came in at 2lbs 13.7oz with poles.
My TX-150 (listed as 3lb 6oz on Clark site). Mine had a pair of 8ft whoopie slings and a pair of 32g biners packed together came in at 2lbs 13.7oz with poles.
That is pretty substantial! I checked in several times and reset the tar (I was using a plastic cake cover as a wide base). I'm still scratching my head.