gnome-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/gnome-calculator - from package: gcalctool

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

On Debian possible default full paths are:

/usr/bin/gnome-calculator - from package: gnome-calculator

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

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