Scale Dynamic Instability

[cafeIKE]

For every day use I have one of those cheap and cheerful 0.1g scales from Harbor Freight.

It is 100% repeatable when a calibration weight is placed on the platform. However, if used to measure directly from the doser, it can be off by as much as -2.5g in 16.

No such error is observed when measuring from a doserless grinder.

I expect this has to do with the energy of a 'load' of coffee hitting the scale, coupled with doser thwacking gforce.

[HB]

Interesting. I tried a couple times dosing directly into the basket sitting on the scale, both perched on the portafilter rest of the Mini E. It was amusing to watch it count up. Anyway, I use a basket out of the portafilter and tare the scale if I want to be super precise.

[erics]

For every day, every shot use, I also have one of those inexpensive 0.1g scales from Harbor Freight.

If I sit the empty basket on the scale and turn the scale on, it "automatically" tares the basket. I spoon the grinds into the basket and, for sure, SOMETIMES notice the problem you describe. I minimize those problems by "PID'ing" my left hand as I add grinds to the basket. Ya, I know, over the top & certified

[CoffeeOwl]

I measured how long it takes to grind my desired dose and now I grind looking at the watch.

[cafeIKE]

I measured how long it takes to grind my desired dose and now I grind looking at the watch.

I gave up on that :

The variabiiity is too great for consistent results

EDIT :
The dose/t line is the dose for a fixed time interval and is the left y-axis
The g/s line is the grams per second and is the right y-axis.
The x-axis is the sample number.

Data collected over 1 week. 15 second grind time.
Hopper kept about 50% full. Same professional roast and batch.
Grinder brushed out at end of day and run for a few seconds to recharge next day.
No additional method employed to remove the grounds from the grinder.

IOW, the grinder was run for 15 seconds and a dose between 11 and 17 grams was delivered.

[CoffeeOwl]

I don't understand the graph.
EDIT:

Ian,
thanks for explanation.
I have not checked mine carefully, but there's one difference: I use a plastic spoon handle to empty all the grinds from the grinder throat.
From my observation (yet, I know - it's not the same as precise measurement) it looks consistent: I grind for 21 seconds to get around 16 grams of coffee, and - I check my timing with an analog watch. I also have a taste for a tighter ristretto from time to time and for that occassion I grind for over a second longer.
As the means of observation serve the volume of tamped coffee (top of puck vs the basket rim) and the flow (and taste).
Maybe empting the throat could improve the consistency? Or am I completely deluded and my 'results' are my imagination? (it would be too much of effort to me to measure it - as I hate trnsfering the grinds to anything after I have it ground, or taking out basket etc. Please someone else measure it for Mazzer, ok?)

[cafeIKE]

Or am I completely deluded and my 'results' are my imagination?

No, you are NOT deluded. Using a tool to remove the retained grounds re-establishes the base line and results are more consistent.