diff --git a/README.md b/README.md
index 1e6c57e..be0aca8 100644
--- a/README.md
+++ b/README.md
@@ -54,12 +54,20 @@ All documentation is built into the prompt. Use the `help` command to view it.
 The conversion operator `to` converts its left argument to the *unit* of its right argument, ignoring its value. For example, `5m to mi` and `5m to 10mi` are identical.
 
 
+## Celsius and Fahrenheit
+
+Celsius and Fahrenheit are not supported as first-class units because they require an offset when converting from other temperature units. This leads to ambiguity when adding units, since one temperature must be seen as a *difference* rather than an absolute temperature.
+
+Daisy instead provides four functions (`fromCelsius`, `toCelsius`, `fromFahrenheit`, `toFahrenheit`) which convert between scalars and Kelvin.
+ - "from" functions take a scalar and return a value in Kelvin: `fromCelsius(0) = 273.15K`
+ - "to" functions take a value in Kelvin and return a scalar: `toCelsius(273.15 K) = 0`
+
+
 ## Multiplication Order
 
 Implicit multiplication has a higher priority than division. `pi/2 radians` will parse as `pi/(2 radians)`. Type `(pi/2) radians` or `pi/2 * radians` to get 90 degrees.
 
 
-
 ## Inline Assignment
 
 The assignment operator `=` returns its value, and can thus be used inside of an expression. For example, `(a = 2) + 2` assigns `a` to `2` and returns `4`. This only works for variable assignment.
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diff --git a/TODO.md b/TODO.md
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--- a/TODO.md
+++ b/TODO.md
@@ -3,7 +3,6 @@
  - list and delete variables
  - Re-evaluate variables (a = q + 2, q = 3, a should evaluate to 5)
  - 2x^-1 as superscript
- - Celsius and Farenheit