Lom,
This thread died in 2005 so its a good idea to say "I'm rezzing an old thread" in your post so folks won't try an assist folks on 13 year old posts as in above.
The unit they sent you helps calibrate the Gauge to Sender over the entire range much the the Classic Instruments SN34 unit.
https://www.jegs.com/i/Classic-Instr.../SN34/10002/-1
Neither will provide dampening of readings due to fuel slosh. My tank has lateral baffle plates which still do no good for gauge needle swings.
The tube sender you have (probably the same PN as mine) has a lot more dampening than a swing arm lever sender or capacitance sender due to the float being internal to the tube and 0.060" drain holes at the top and bottom of the tube effectively slowing changes.
Mine was sticking in various positions so I installed a Programmable Speedhut fuel gauge but still had the sticking issue.
I changed the sender (PN VDO 224-221 SENDER FUEL DIP PIPE 54MM L 210MM) and now all is good.
I'd check with the Backdraft folks on the PN though since mine is a very early car.