#!/bin/bash

DATAFILE=/tmp/fake-datafile

#-----  collect the datas
> ${DATAFILE}
for s in $(seq 1 20)
do
    v=$(./fake-values -s -t 1 2> /dev/null)
    echo $s $v >> ${DATAFILE}
done

#-----  do dome useless computations
awk	'
	NR==1	{ debut = $2 }
		{ print $2-debut, $3 }
	'                                   \
< ${DATAFILE}