I can set 0 new cards / day or 1 new card / day, but is there a way to set 0.33 new cards / day (= 1 new card every 3 days)?
No, 1 card per day is the minimum (except for 0, of course).
Thereās no practical difference between learning one new card every three days and doing nothing at all, haha.
Just joking, if for some reason you just need that, you can manually set new cards to 0 a and change that value to 1 every three days. Yes, itās not an automatic process, but it takes less than 5 seconds.
Good idea and Instead of changing it back and forth, this can be done with the ācustom studyā and then āIncrease todayās new card limitā options.
Just as a matter of interest
How many new cards were actually added in the last 30 days,
How do I figure that out?
Search this in the browser: added:30
That command returns all 105 of them.
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With functionality to present one new card every 3 days, then you would have seen 10 new cards in those 30 days.
The remaining 95 cards would be presented over the following 285 days.
You probably have your own reasons for taking 10 1/2 months to actually see 105 new cards.
Good luck 
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Yes, Iām learning the organ using this deck. I canāt learn a new piece everyday, but only a few per week.
Thereās another option then, suspend all the cards that havenāt been seen yet, then set a reminder in a calendar app to unsuspend a card every 3 days. I know itās a bit more cumbersome, but you also get more of a choice over the card you see.
From what I can see, the cards only tell you what to practice/play, and are not used to memorise anything, right? So accidentally seeing their contents in the browser while unsuspending wonāt be an issue at all.
correct
Since Anki is not intended to be used like this, Iām afraid you may encounter other problems as well. Most notably, the scheduling algorithm was designed for active recall testing with small pieces of information. Practising an instrument is an entirely different matter.
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But, IMHO, the OP needs to grade the card as Again, Hard, Good, or Easy, and then suspend the card again. Right? For the SRS?
Or do they delete that card because it only needs to be seen once? In that case, only the calendar app is needed. Anki provides nothing.
I think the post by @shallash (#11) gives the most information about what the OP is actually trying to do. It might take us about 10 1/2 months to get any remaining info piecemeal from the OP - using red-hot pliers ![]()