The ratio pyrometer optris CTratio 1M is largely insensitive to dust, fumes and soiled sight glasses. This means that measurements remain accurate even when the degree of soiling of the sight glass exceeds 90 percent. The pyrometer also delivers reliable measurements if the target object fills only 5 % of the spot size, or if it moves very rapidly. This ratio pyrometer is especially suited for measuring high temperatures on metals and for monitoring high-speed processes.