I've seen the light! I will return to just mixing my juice with this scale, accurate or inaccurate as it may be, until a real problem arises

I share your frustration my friend!

My obsessive need to be right, or at least as "right" as I am willing to be (yeah... yeah... yeah... I know;
that bar is set without any vertical challenge!

), sent me down a similar rabbit hole. When I started seeing all the uncontrolled (by me) variables, I decided to return to my ostrich stance (head firmly in sand), and ignore calibration.
My "average drops" seem to weigh in the neighborhood of 0.03g. As long as they stay in this vicinity; I am satisfied. When that starts getting sketchy, I will either start trying to figure out how to re-calibrate it, or shop for a new scale.
BTW, I am assuming equally cheap weights from Amazon are no more accurate then Ebay or Yahoo.
TL;dr (short answer): yes.
If you are in the mood for some dry technical reading, this sales brochure (by Fisher Scientific) well tell you more than you ever wanted to know about calibration weights:
https://static.fishersci.com/cmsass...c/pdf/MettlerToledo/11796035_OIML_weights.pdf
For abreviated reading, check out page 13, which lists all the acceptable tolerances for all the IOML, ANSI, and ASTM industry standards. Any seller that
does not specify a specific certification level; I would personally assume "at or above" the highest variation. Others may feel different.
Man, you had me a little nervous at this point!
Yeah... I kind of paused as I was writing that sentence. The "gentle Joel" in me said this might set off a few alarms, the "evil Joel" said to go ahead and tug your chain a little, and then the "gentle Joel" said that the actual question could not possibly be worse than your imagination, and thereby soften any potential offense. Bottom line; it was kinda cruel, but I am glad you saw the humor in it.
We have no pharmacist in this small town and I get my Part D (or whatever it's called) meds through the mail......so no and I don't even have a name. But I may check around for anybody that may have a scale I could check a 200g and 500g calibration weight if that turns out to be what I need. But at the cost of those two weights, I could just buy another scale. Back-ups for our back-ups, right?
I don't know what you have, in the way of industry or educational institutions, in your area. But, I would be looking for colleges, scientific businesses, gems/precious metal dealers, research, and/or medical fields... anyone that might have need for certification-level scale use. The idea of colleges and universities, that have research or industrial programs, stand out in my mind. Professors tend to be very accommodating, if you can catch them during office hours.
If you ever do get it figured out, I would be curious to know your results, as I use the SF-400D as well.
One last tidbit of useless info, if you feel like dealing with folks in China; I figured out who actually manufactures our scales. They are SuoFei and their homepage is
Chinese Oem- Electronic scales,Kitchen Scale,Hook scales,Human scale-JiangYin SuoFei Electronic Technology Co.,Ltd.
I don't have the patience/motivation to try that route; but you may feel differently. This is their link for our specific scale:
JiangYin SuoFei Electronic Technology Co.,Ltd.
In any case, I am glad you have found (at least)
some peace about it.

