diff --git a/data/calcurse.md b/data/calcurse.md
new file mode 100644
index 0000000..afebbfc
--- /dev/null
+++ b/data/calcurse.md
@@ -0,0 +1,9 @@
+---
+title: "calcurse"
+tags: [ "data", "calendar", "daylight savings" ]
+---
+
+## Setup
+
+The UK government keeps an ics file with clock, [here](https://www.gov.uk/when-do-the-clocks-change/united-kingdom.ics).
+
diff --git a/data/radicale.md b/data/radicale.md
new file mode 100644
index 0000000..d6586ed
--- /dev/null
+++ b/data/radicale.md
@@ -0,0 +1,126 @@
+---
+title: "radicale and nginx"
+tags: [ "data", "calendar" ]
+---
+
+Check before you start:
+
+- you have a normally running site on nginx already.
+- your server has the directory `/etc/nginx/sites-enabled/` enabled in the nginx config.
+
+## Installation and Service
+
+Install `radicale` through your package manager (not `pip`).
+The standard `radicale` package should come with a nice `systemd` service file.
+
+If the service comes already-started, stop it immediately:
+
+```bash
+sudo systemctl stop radicale
+```
+
+## Set up Passwords
+
+Edit `/etc/radicale/config`, changing the `[auth]` section from this:
+
+```
+#type = none
+```
+
+...to this:
+```
+#type = htpasswd
+```
+
+If the service is started, restart it to make sure nobody can sign in without a password.
+
+
+Next, find the `htpasswd` program.
+You might get it in the `apache` package or similar.
+
+`htpasswd` allows you to generate passwords for users, and place them in `/etc/radicale/users`.
+
+```bash
+PASS="$(xkcdpass)
+htpasswd -nb $USER "$PASS" | sudo tee -a /etc/radicale/users
+echo "Your username is $USER"
+echo "Your password is $PASS"
+```
+Right now, you can't sign into the server except through the localhost, which is pointless.
+So now we add a subdomain to `nginx`.
+
+```nginx
+
+echo '
+ server {
+    if ($host = cal.DOMAIN) {
+        return 301 https://$host$request_uri;
+    } # managed by Certbot
+
+
+     listen 80;
+     server_name cal.DOMAIN;
+                                                                                        
+     location / {
+         proxy_pass http://localhost:5232;
+         proxy_set_header Host $host;
+         proxy_set_header X-Real-IP $remote_addr;
+         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+     }
+                                                                                        
+     return 301 https://$server_name$request_uri;
+ 
+
+}
+                                                                                        
+ server {
+     listen 443 ssl;
+     server_name cal.DOMAIN;
+    ssl_certificate /etc/letsencrypt/live/cal.DOMAIN/fullchain.pem; # managed by Certbot
+    ssl_certificate_key /etc/letsencrypt/live/cal.DOMAIN/privkey.pem; # managed by Certbot
+                                                                                        
+     location / {
+         proxy_pass http://localhost:5232;
+         proxy_set_header Host $host;
+         proxy_set_header X-Real-IP $remote_addr;
+         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+     }
+ 
+}
+' > /etc/nginx/sites-available/radicale
+sudo ln -s /etc/nginx/sites-available/radicale /etc/nginx/sites-enables/
+```
+
+Finally, replace the example `DOMAIN` with your actual domain name.
+
+```bash
+DOMAIN=whatever.com
+sudo sed -i "s/DOMAIN/$DOMAIN/g" /etc/nginx/sites-available/radicale 
+
+```
+
+(optional: replace that `cal.` prefix with anything else)
+
+Check nginx is happy:
+
+
+```bash
+sudo nginx -t
+```
+You will almost certainly need a new SSL certificate for the site:
+
+```bash
+sudo certbod -d cal.$DOMAIN
+```
+
+Start or restart both services:
+
+
+```bash
+sudo systemctl start radicale
+sudo systemctl restart nginx
+```
+
+You should now be able to log into your calendar, and add it to a phone.
+
+NB: you don't need the port number.
diff --git a/system/bash_tricks.md b/system/bash_tricks.md
index 67226ef..c1e05b7 100644
--- a/system/bash_tricks.md
+++ b/system/bash_tricks.md
@@ -1,6 +1,6 @@
 ---
-title: "Terminal Tips"
-tags: [ "Documentation", "System" ]
+title: "bash tips"
+tags: [ "Documentation", "Shell", "POSIX" ]
 ---
 ## Track Live Changes
 
@@ -67,6 +67,18 @@ Add number to variables with:
 
 `((n--))` works identically.
 
+### POSIX WARNING
+
+The number commands above work in `bash`, but not in bare-ass POSIX shells, such as `dash`.
+
+Instead, you might do:
+
+```sh
+x=2
+x=$(( x +1 ))
+x=$(( x*x ))
+```
+
 ## Finding Duplicate Files
 
 ```bash
@@ -97,3 +109,8 @@ That gives you a random directory to mess about in.
    cd $dir
 ```
 
+### POSIX WARNING
+
+These smart-brackets are a bash feature.
+If you try to use `{A..Z}` in dash, it will think of this as a single item.
+
diff --git a/vision/imagemagick.md b/vision/imagemagick.md
index 75c76b8..1456ea4 100644
--- a/vision/imagemagick.md
+++ b/vision/imagemagick.md
@@ -2,7 +2,6 @@
 title: "imagemagick"
 tags: [ "Documentation", "Vision" ]
 ---
-[Source](http://lxlinux.com/imagemagick.html)
 
 Convert jpg to png.
 
@@ -41,13 +40,13 @@ convert image.jpg -resize 25% output.jpg
 
 # Trim images to border
 
-This is generally used for transparrent images.
+This is generally used for transparent images.
 
 ```bash
 convert -trim image.png output.png
 ```
 
-Make the white of an image transparrent.
+Make the white of an image transparent.
 
 ```bash
 convert -transparent white -fuzz 10% input.png output.png
@@ -101,7 +100,7 @@ See your installed fonts:
 convert -list font
 ```
 
-Make na image showing day of the week:
+Make an image showing day of the week:
 
 ```bash
 convert -fill blue -font Sauce-Code-Pro-Semibold-Nerd-Font-Complete-Mono -gravity center -pointsize 79 label:$(date +%A) day.png