[rink/en] Add Rink tool

rink.md

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+---
+category: tool
+name: Rink
+contributors:
+  - ["Evan Hahn", "https://evanhahn.com/"]
+filename: LearnRink.txt
+---
+
+[Rink](https://rinkcalc.app/about) is a unit-aware calculator for the command
+line and [the browser](https://rinkcalc.app/).
+
+Start the Rink REPL with `rink`, or run a calculation with
+`rink '10 pounds to kilograms'`.
+
+Rink values are numbers with units:
+
+```
+> 123 kilometers
+123 kilometer (length)
+
+> 1.5 radians
+1.5 radian (angle)
+```
+
+You don't _need_ units, though. Values can be "dimensionless":
+
+```
+> 123
+123  (dimensionless)
+
+> -456.78
+-456.78  (dimensionless)
+```
+
+Rink supports arbitrary precision:
+
+```
+> 2/3 * 1/6
+0.[1]...  (dimensionless)
+
+> 1e20000 / 2e20001
+0.05  (dimensionless)
+```
+
+Convert units, including currencies:
+
+```
+> 10 pounds to kilograms
+approx. 4.535923 kilogram (mass)
+
+> 32 degF to degC
+0 °C (temperature)
+
+> 1 KiB to B
+1024 byte (information)
+
+> 2 halfnotes to wholenote
+1 wholenote (musical_note_length)
+
+> 1 EUR to INR
+97.4838 INR (money)
+
+> 52 weeks to seconds
+31449600 second (time)
+```
+
+You can use `->` instead of `to`, which can be easier to read:
+
+```
+> 52 weeks -> seconds
+31449600 second (time)
+```
+
+Do math with units:
+
+```
+> 1.5 hours + 30 minutes
+2 hour, 0 second (time)
+
+> 100 GB / 25 mbps
+8 hour, 53 minute, 20 second (time)
+```
+
+Combine math with unit conversion:
+
+```
+> 12 megabytes + 34 kilobytes + 56 bytes -> bytes
+12034056 byte (information)
+```
+
+Convert a time to another time zone:
+
+```
+> #2025-04-20T18:09 America/Chicago# -> "Africa/Lagos"
+2025-04-21 00:09:00 WAT
+
+> #01:23# -> "America/Sao_Paulo"
+2019-01-23 05:23:00 -02
+
+> now -> "Asia/Yangon"
+2019-01-23 17:26:00 +0630
+```
+
+Compute time deltas:
+
+```
+> #2025-01-23# - #2024-02-10#
+49 week, 5 day, 0 second (time)
+
+> #2025-01-23# - #2024-02-10# -> day
+348 day (time)
+
+> #2025-01-23# - #2024-02-10# -> hour
+8352 hour (time)
+
+> now - #2025-01-01# -> day
+109 day (time)
+```
+
+Math with time deltas:
+
+```
+> now + 3 days
+2020-01-26 01:23:00 +00:00
+
+> now - (four score years + seven years)
+1933-01-22 23:40:20.182200 +00:00 (92 years ago)
+```
+
+Remember that _months and years are weird_ (at no fault of Rink).
+Compare Rink's default `year` and `month` units to alternate ones:
+
+```
+> 1 year -> days
+approx. 365.2421 day (time)
+
+> 1 calendaryear -> days
+365 day (time)
+
+> 1 month -> days
+approx. 30.43684 day (time)
+
+> 1 lunarmonth -> days
+approx. 29.53058 day (time)
+```
+
+Work with percentages:
+
+```
+> 0.25 -> percent
+25 percent (dimensionless)
+
+> 25 percent
+0.25  (dimensionless)
+
+> 100 meters * 25 percent
+25 meter (length)
+```
+
+Use helpers like "billion" and "thousand":
+
+```
+> 1 billion / 1 million
+1000  (dimensionless)
+
+> 1 billion kilograms / 1 million pounds
+approx. 2204.622  (dimensionless)
+```
+
+Convert numbers between bases, such as hexadecimal and binary:
+
+```
+> 0x45
+69  (dimensionless)
+
+> 0b1010011010
+666  (dimensionless)
+
+> 420 -> base 16
+1a4  (dimensionless)
+
+> 420 -> hex
+1a4  (dimensionless)
+
+> 420 -> base 2
+110100100  (dimensionless)
+
+> 420 -> bin
+110100100  (dimensionless)
+```
+
+Use simple math functions, like square root.
+_Note that these do not use arbitrary precision._
+
+```
+> sqrt(4)
+approx. 2  (dimensionless)
+
+> sqrt(4) meters
+approx. 2 meter (length)
+```
+
+Rink supports a number of constants, such as the volume of celestial bodies:
+
+```
+> volume of uranus / volume of moon
+approx. 3111.849  (dimensionless)
+```
+
+## Further Information
+
+- [Rink homepage](https://rinkcalc.app/about)
+
+- [`rink` manpage](https://rinkcalc.app/manual)