diff --git a/README.md b/README.md
index b83795c..44a1857 100644
--- a/README.md
+++ b/README.md
@@ -821,20 +821,36 @@ You can use `geval` to initiate a [Gonito](https://gonito.net) challenge:
 Of course, any other metric can
 be given to generate another type of toy challenge:
 
-    geval --init --expected-directory my-machine-translation-challenge --metric BLEU
+    geval --init --expected-directory my-machine-translation-challenge --metric BLEU --precision 4 -% -B 200
+
+Note that the `--precision 4` and `-%` options give you pretty
+formatting of evaluation scores. Simply you don't want ugly scores
+such as `0.1729801323401`! The `--precision 4` option limits it to 4
+digits after the decimal dot (`0.1730`) and `-%` makes it into a
+percent-like value (`17.30`).
+
+The `-B 200` is yet another interesting option. If it is used, GEval will
+calculate confidence intervals using bootstrap sampling.
 
 ### Preparing a Git repository
 
 [Gonito](https://gonito.net) platform expects a Git repository with a
 challenge to be submitted. The suggested way to do this will be
 presented as a [Makefile](https://en.wikipedia.org/wiki/Makefile), but
-of course you could use any other scripting language and the commands
-should be clear if you know Bash and some basic facts about Makefiles:
+of course you could use any other scripting language (anyway, it's
+always a good idea to start with `geval --init` and then add/overwrite
+the files). The commands should be clear if you know Bash and some
+basic facts about Makefiles:
 
 * a Makefile consists of rules, each rule specifies how to build a _target_ out of _dependencies_ using
   shell commands
 * `$@` is the (first) target, whereas `$<` — the first dependency
-* the indentation should be done with TABs, not spaces!
+* the indentation should be done with **TABs, not spaces**! (see the
+  [file with TABs](misc/challenge-preparation-example/Makefile)
+
+Also don't forget to compress aggressively large files (e.g.
+`train/in.tsv` and `train/expected.tsv`), the xz compressor is a good
+option and is handled by GEval.
 
 ```
 SHELL=/bin/bash
diff --git a/misc/challenge-preparation-example/Makefile b/misc/challenge-preparation-example/Makefile
new file mode 100644
index 0000000..304ab44
--- /dev/null
+++ b/misc/challenge-preparation-example/Makefile
@@ -0,0 +1,78 @@
+SHELL=/bin/bash
+
+# no not delete intermediate files
+.SECONDARY:
+
+# the directory where the challenge will be created
+output_directory=...
+
+# let's define which files are necessary, other files will be created if needed;
+# we'll compress the input files with xz and leave `expected.tsv` files uncompressed
+# (but you could decide otherwise)
+all: $(output_directory)/train/in.tsv.xz $(output_directory)/train/expected.tsv \
+     $(output_directory)/dev-0/in.tsv.xz $(output_directory)/dev-0/expected.tsv \
+     $(output_directory)/test-A/in.tsv.xz $(output_directory)/test-A/expected.tsv \
+     $(output_directory)/README.md \
+     $(output_directory)/in-header.tsv \
+     $(output_directory)/out-header.tsv
+	# always validate the challenge
+	geval --validate --expected-directory $(output_directory)
+
+# we need to replace the default README.md, we assume that it
+# is kept as challenge-readme.md in the repo with this Makefile;
+# note that the title from README.md will be taken as the title of the challenge
+# and the first paragraph — as a short description
+$(output_directory)/README.md: challenge-readme.md $(output_directory)/config.txt
+	cp $< $@
+
+# prepare header files (see above section on headers)
+$(output_directory)/in-header.tsv: in-header.tsv $(output_directory)/config.txt
+	cp $< $@
+
+$(output_directory)/out-header.tsv: out-header.tsv $(output_directory)/config.txt
+	cp $< $@
+
+$(output_directory)/config.txt:
+	mkdir -p $(output_directory)
+	geval --init --expected-directory $(output_directory) --metric MAIN_METRIC --metric AUXILIARY_METRIC --precision N --gonito-host https://some.gonito.host.net
+	# `geval --init` will generate a toy challenge for a given metric(s)
+	# ... but we remove the `in/expected.tsv` files just in case
+	# (we will overwrite this with our data anyway)
+	rm -f $(output_directory)/{train,dev-0,test-A}/{in,expected}.tsv
+	rm $(output_directory)/{README.md,in-header.tsv,out-header.tsv}
+
+# a "total" TSV containing all the data, we'll split it later
+all-data.tsv.xz: prepare.py some-other-files
+	# the data are generated using your script, let's say prepare.py and
+	# some other files (of course, it depends on your task);
+	# the file will be compressed with xz
+	./prepare.py some-other-files | xz > $@
+
+# and now the challenge files, note that they will depend on config.txt so that
+# the challenge skeleton is generated first
+
+# The best way to split data into train, dev-0 and test-A set is to do it in a random,
+# but _stable_ manner, the set into which an item is assigned should depend on the MD5 sum
+# of some field in the input data (a field unlikely to change). Let's assume
+# that you created a script `filter.py` that takes as an argument a regular expression that will be applied
+# to the MD5 sum (written in the hexadecimal format).
+
+$(output_directory)/train/in.tsv.xz $(output_directory)/train/expected.tsv: all-data.tsv.xz filter.py $(output_directory)/config.txt
+	# 1. xzcat for decompression
+	# 2. ./filter.py will select 14/16=7/8 of items in a stable random manner
+	# 3. tee >(...) is Bash magic to fork the ouptut into two streams
+	# 4. cut will select the columns
+	# 5. xz will compress it back
+	xzcat $< | ./filter.py '[0-9abcd]$' | tee >(cut -f 1 > $(output_directory)/train/expected.tsv) | cut -f 2- | xz > $(output_directory)/train/in.tsv.xz
+
+$(output_directory)/dev-0/in.tsv.xz $(output_directory)/dev-0/expected.tsv: all-data.tsv.xz filter.py $(output_directory)/config.txt
+	# 1/16 of items goes to dev-0 set
+	xzcat $< | ./filter.py 'e$' | tee >(cut -f 1 > $(output_directory)/dev-0/expected.tsv) | cut -f 2- | xz > $(output_directory)/dev-0/in.tsv.xz
+
+$(output_directory)/test-A/in.tsv.xz $(output_directory)/test-A/expected.tsv: all-data.tsv.xz filter.py $(output_directory)/config.txt
+	# (other) 1/16 of items goes to test-A set
+	xzcat $< | ./filter.py 'f$' | tee >(cut -f 1 > $(output_directory)/test-A/expected.tsv) | cut -f 2- | xz > $(output_directory)/test-A/in.tsv.xz
+
+# wiping out the challenge, if you are desperate
+clean:
+	rm -rf $(output_directory)