Part of the sales pitch for investing in a modern all-glass upgrade like the Dynon SkyView or Garmin G3X Touch system is the ultimate weight savings that tags along with the project. Sure, yanking out the vacuum system and the round-gauge gyros in favor of electronic instruments generally will yield a sizable weight savings. But just because the new weight and balance report shows more useful load doesn’t necessarily mean the numbers are accurate. In fact, that new report can be grossly inaccurate.
Unless the aircraft has never been modified (which is highly unlikely for older models), there is a good chance there are at least some discrepancies in its weight and balance data. A common phrase written in aircraft maintenance logbooks after the job is done is “negligible change to weight and balance.” That may be a true statement from a regulatory standpoint because in general, if the item installed or removed was under one pound many installers won’t generate a new weight and balance report.