Ok! First off, I've been at this airplane stuff as an A&P/IA for 40 years!- no kidding. yep, so when I see something off it drives me nuts. I wanted to research others within my week break between weighing) For example, back in 05, I weighed my craft (73 PA28150 Cruiser with Piper Air (
www.joespiper.com) and the mains were very close - 5 lb spread. Over the years I have removed and added various equipment and accessories. I also repainted the craft (colors only) recently, added ADS-B (978 in/out wifi), PFS exhaust,new Skytech started (huge weight savings), removed AC air compressor and bracket (26 lbs off the nose). Total 35 lbs off nose.
Time to reweigh airplane. Mind now, I am using digital scales to 1/10th % tolerance (extremely accurate with indicated percentage weights as well - all percentages must equal 100%). Drained tanks empty (mandatory), set the plane up, removed tail satnd and weighed it - 30 Lb spread between mains (Lft - 539, Rt - 509, Nose - 402: (rocked wings for stable, same - WTF?
Why is spread important - roll balance with equal fuel each tank. You ATP people know this. Anyhoo, I reweighed - same thing. So, took a break, following week. Removed head sets, and quart of oil from left seat (6 lbs). Reset scales - zero weight, rocked wings to equalize struts EQUAL length (key), and also set prop to vertical position (key) - WALA! Actually, opening the door (swinging it) has an affect on the weights as well, but we fly with door closed. So, with the craft set aligned laterally and longitudinally ( my mistake - no brainer / happens!) and refilling tires all to 25 psig (important) the weights came out as they should Nose - 396, Rt - 517, Lft - 528 (12 lb spread). I can now sign off new weight and balance with annual. I must have been having a bad day that initial weigh day. That's why we do things over and over until its right and not until then. That is also why I am very concerned about the FAA wanting to change training rules be it pilot or mechanic to skip corners to please business for profits - its killing people (so far recent 2 Boeing 737's)
Answered my question, hope it answers yours
All about the setup or in flight - sterile cockpit and checklists. On the ground you get a second chance, in the air, might be a flip of the coin!