The ECH Ro is a long-delay electrochemical fuze.
Operation principle is electrochemical dissolving of wire by means of electrical current.
Dissolving rate is strictly proportional to passing current. By choosing value of resistor (by clamps) in the circuit, value of current and thus speed of dissolving is set.
Blue ampoule contains electrolyte, which is to be poured into electrolytic chamber prior to activating the fuze.
Electrical power is provided by standard zinc army battery (D-cell), non-freeze type.
When wire is dissolved enough, force of spring breaks it and striker activates the primer.
Information thanks to Tomáš.