diff --git a/doc/erko_howto_tools.txt b/doc/erko_howto_tools.txt
index e7671f583dd855a8cf772464598ae3c1a087dd89..12cf2dacce1a83c871c0eb1679d3e35268145169 100755
--- a/doc/erko_howto_tools.txt
+++ b/doc/erko_howto_tools.txt
@@ -182,6 +182,8 @@ git add <dir>/<file>       # add to stage area, set for commit. Cannot add empty
 git add .                  # add all new and modified to stageing area
 git diff                   # diff between file in working tree and staging area
 git diff --staged          # diff between file in staging area and history
+git difftool -t meld       # GUI frontend for git diff, with --no-prompt to avoid Y/n prompt request to launch meld
+git difftool -t meld --no-prompt   # e.g. define alias gitmeld
 git rm <filename>          # remove file from working tree and stage the delete
 git checkout -- <filename> # revert a working tree change
 git reset                  # clear stage area
@@ -373,72 +375,8 @@ for me it is an ok workaround,
 * Markdown
 *******************************************************************************
 
-Use e.g.:
-- Linux 'retext' as markdown editor and previewer. 
-- https://typora.io, mooi maar waarscijnlijk te geavanceerd en daardoor niet
-  compatible met andere viewers
-- Python3 --> import mdutil  # markdown writer en reader
-
-Markdown is not well defined, so it is not always sure that the text will 
-appear as expected in each viewer. For example retext and gitlab viewer differ.
-Therefore it is important to keep the markdown simple and to accept that
-readable text is good enough, rather than to strive for a specific layout.
-
-Text will wrap.
-
-Backslash is escape chararcter.
-
-# Heading 1
-## Heading 2
-### Heading 3
-#### Heading 4
-##### Heading 5
-###### Heading 6
-
-Horizontal rules three or more of ***, ___, ---
-
-*italic*
-_italic_
-**bold**
-__bold__
-**bold and _bolditalic_**    combined
-`boxed`
-~~strike through~~
-
-```vhdl
-Text in ascii VHDL style for GitLab
-```
-
-Block quotes (alinea with an indent bar):
-> Block text will wrap
-
-Unordered list using *, -, +, indent >= 1 space
-* Main item 1
-* Main item 2          
- * sub item 2a  use 2 trailing spaces for return inside paragraph
- * sub item 2b
- 
-Ordered list 
-1. Main item 1
-2. Main item 2          
- 2.1 sub item 2a
- 2.2 sub item 2b
-           
-Images  
-![Logo](path to image file)
-![Logo](web link to image file)
-![Logo][image1]
-
-[image1]:web link to image file
-
-Links:
-[ASTRON]:https://www.astron.nl
-
-Table:
-|col1 | col2| Col3 |    column titles
-|---|:---:|--:|    >= 3 dashes, colon for left, center, right align
-| row text | row text | row text|
-| row text | row text | row text|
+See https://git.astron.nl/desp/args/Markdown/readme_markdown.txt 
+
 
 *******************************************************************************
 * vi
@@ -481,6 +419,10 @@ bcksp    |
   
   Note: Windows NTSERVER65 has IP: 10.87.3.165
 
+* Login using ssh keys:
+
+https://www.digitalocean.com/community/tutorials/how-to-configure-ssh-key-based-authentication-on-a-linux-server
+
 * For ssh access from home without manual hop via the kooistra@portal.astron.nl, put this in $HOME/.ssh/config:
 
 Host *
@@ -705,8 +647,12 @@ Quartus version meeting minutes 13 may 2020 (RW, LH JH, EK):
 * Linux
 *******************************************************************************
 
+https://regexr.com/
+
 https://linuxize.com/
 
+> passwd
+
 # Linux update via
 # - system updates available icon and notifications icon in toolbar
 # - of via command line:
@@ -822,3 +768,6 @@ https://intranet.astron.nl/diensten/ict/manuals-and-documents/manuals-and-docume
 
 pycharm
 https://pypi.org/project/black/ # Python code formatter
+
+numpy tutorial:
+https://lwn.net/SubscriberLink/847039/3016fa7278000b77/