Extech instruments tm20 tm25 waterproof wall mountable temperature indicators extech tm25 the extech instruments tm25 is a waterproof portable wall mountable temperature indicator this indicator has been designed and manufactured for measuring the temperature of air liquid paste or semi solid materials the tm25 is equipped with a penetration probe for insertion into materials under test the tm25 comes with a removable foot and magnetic back it can easily be used on your desktop or