Calculator: 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/Calculator - from package: gnustep-examples

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

On Debian possible default full paths are:

/usr/bin/Calculator - from package: gnustep-examples

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

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