calibrate_ppa: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/calibrate_ppa - from package: pnm2ppa

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/calibrate_ppa - from package: printer-driver-pnm2ppa

You may install the required package with command apt-get install {package}

Error in other languages:
calibrate_ppa: bevel nie gevind nie
calibrate_ppa: comandă negăsită
calibrate_ppa: comando não encontrado
calibrate_ppa: commande introuvable
calibrate_ppa: command not found
calibrate_ppa: käsku ei ole
calibrate_ppa: không tìm thấy lệnh
calibrate_ppa: komanda nerasta
calibrate_ppa: Kommando nicht gefunden.
calibrate_ppa: kommandot finns inte
calibrate_ppa: komut yok
calibrate_ppa: nie znaleziono polecenia
calibrate_ppa: níor aimsíodh an t-ordú
calibrate_ppa: no se encontró la orden
calibrate_ppa: no s'ha trobat l'ordre
calibrate_ppa: opdracht niet gevonden
calibrate_ppa: parancs nem található
calibrate_ppa: perintah tidak ditemukan
calibrate_ppa: príkaz nenájdený
calibrate_ppa: příkaz nenalezen
calibrate_ppa: команда не найдена
calibrate_ppa: командата не е открита
calibrate_ppa: 命令找不到
calibrate_ppa: コマンドが見つかりません