[elpa] externals/speedrect 8902387c85 28/90: README: describe operation with calc

[ELPA Syncer]

branch: externals/speedrect
commit 8902387c85f7934484caf766f9c05376d3e8be0d
Author: JD Smith <93749+jdtsmith@users.noreply.github.com>
Commit: JD Smith <93749+jdtsmith@users.noreply.github.com>

    README: describe operation with calc
---
 README.md | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/README.md b/README.md
index 3d9317c2bf..4d12a75043 100644
--- a/README.md
+++ b/README.md
@@ -36,10 +36,23 @@ Or, with `use-package` and `straight`:
 
 Start `rectangle-mark-mode` as usual (`C-x SPC`, by default).  Hit `?` to 
summon a help buffer of available key bindings.
 
+
 ## Hints
 
 A rectangle is just a _region_ (point and mark), specially interpreted.  While 
marking rectangles, you can `C-x C-x` to switch point and mark to make changes 
to the top/bottom of the selected region.
 
+## Using Calc
+
+[Calc](https://www.gnu.org/software/emacs/manual/html_mono/calc.html) is an 
ancient and powerful calculator in emacs with many capabilities.  In addition 
to simple sums, `SpeedRect` offers powerful two-way communication with calc:
+
+1. It can send columns of numbers to calc as a _matrix_ (2D array of numbers). 
 Once in calc, you can operate on those numbers using a wide array of 
operations.  Many of these "just work" on matrices (e.g. `1 +` will add one to 
all the numbers).  Others can easily be mapped over matrix elements (try `v 
m`). 
+2. Once you have something you're happy with at the top of calc's *stack* (the 
entry number `1:`), you can:
+  - hit `q` to return to your buffer (where `rectangle-mark-mode` will still 
be active),
+  - adjust the position of your rectangle if needed (`S-left/right` is useful 
for this), and
+  - hit `m` to copy the top calc matrix over the top of the marked rectangle 
(first checking that it has the right number of rows).
+
+Note: what you see is what you get in calc.  `v [` and `v ,` will remove the 
brackets and commas.  `v >` will right align numbers.  `d f` will let you set 
the number of digits after the decimal.  And many more options.  
+
 ## Key Listing
 
 ```