Tare tags: A better way to do odometer resets

[dreeves]

### Desiderata
- [ ] Implement this
- [ ] Tweet the UVI(s)
- [ ] Unsnooze https://github.com/beeminder/beeminder/issues/2561

Instead of the odometer reset feature, you should mark datapoints as "TARE". Say a datapoint with value v is marked as a tare and let u be the previous y-value before v was entered. Then the actual value of v is disregarded (but remembered). The plotted value corresponding to v is still u and subsequent datapoints are measured as the delta from v and added to u. For example:

value entered	value plotted	note
0 TARE	0	doesn't matter if explicit TARE tag on initial "0"
20	20	first real datapoint
50	50	if this were kyoom-y we'd plot "70" but it's not
0 TARE	50	traditional odometer reset
10	60	odometer shows 10 + previous 50 = 60 total
15	65	again, add 50 to current odometer reading
100 TARE	65	ignore current reading of "100" but remember it
140	105	40 added from previous 100 so add it to 65

Or for the case of an initial nonzero datapoint:

value entered	value plotted	note
30 TARE	0	starting at "30" but treating it as zero
35	5	adding 5 since previous taring
40	10	and another 5 for 10 total

// -----------------------------------------------------------------------------
// Take a list of entered datapoint values, d, and a parallel list of booleans
// for whether to tare the corresponding value, t. Return the list of y-values.
function tareify(d, t) {
  let cd = 0 // cumulative delta to subtract
  return d.map((x, i) => {
    if (t[i]) cd += x - (i === 0 ? 0 : d[i-1])
    return x - cd
  })
}

This is a much better way to do the things described at https://forum.beeminder.com/t/restarting-odometer-to-non-zero-value/299/17?u=dreev

Cognata

• https://github.com/beeminder/beeminder/issues/2561
• https://github.com/beeminder/beeminder/issues/2423
• https://github.com/beeminder/beeminder/issues/2209
• http://tareable.com

Verbata: tare tags, death to the magical odometer reset feature, anti-magic violations,

[dreeves]

HT Madge Castle for possible syntax for this (and making an exhaustive list of the possibilities!).

The best candidate is like =120 which you can think of as overriding what's there with 120.

Madge's exhaustive list

* `=120` seems like the obvious choice; interpret as override what's there with 120 * `@120` like setting it "at" 120, though also reads as tagging/at-mentioning * `+120` no, arithmetic symbol * `-120` no, arithmetic symbol * `.120` no, arithmetic symbol * `/120` no, arithmetic symbol * `*120` no, arithmetic symbol * `~120` reads as "approximately" * `?120` seems like a tentative data point * `!120` reads as both "not" and, like, "alt-universe fanfic" (like barista!Draco), but also, "force it to this" * `#120` conflicts with hashtagging * `$120` conflicts with the money side of Beeminder aesthetically * `^120` conflicts with "today" syntax * `&120` i would interpret as "don't reset my odometer but i'm adding an extra 120" * `"120` conflicts with datapoint comment syntax (and looks ugly) * `'120` no, unbalanced * `` `120 `` no, unbalanced * `(120` no, unbalanced * `)120` no, unbalanced * `[120` no, unbalanced * `]120` no, unbalanced * `{120` no, unbalanced * `}120` no, unbalanced * `<120` no, unbalanced * `>120` no, unbalanced * `_120` sets the new "floor" to 120? but parses as a variable name; seems weird * `:120` conflicts with HH:MM:SS * `;120` kinda ugly * `|120` no * `,120` no, especially since commas are decimal points in some places

But... the expedient way to do this is with a magic hashtag (not to be confused with the bad kind of magic) in the datapoint comment.

[dreeves]

This has been coming up more lately. Bee is beeminding reading a stack of books, which mostly the existing odometer reset feature works fine for but one of the books she previously read like a 100 pages of so she wants to hit tare at page 100.

And then talking about this in the Discord today, how we really want the old feature from Draft for beeminding words added plus words deleted. I said:

if we add this #TARE tags feature, i think the workflow would be like so:

1. have an URLminder goal for wordcount on a document
2. compose, indite, lucubrate
3. hit auto-fetch to make sure beeminder has the latest wordcount
4. delete a chunk of text
5. hit TARE
6. go to step 2
7. if you forget step 3, retrieve it or paste an equivalent block of text into a scratch area and then go to step 3