Abstract: The invention provides an ammeter specially suited for measuring the currents passing in high voltage, high power A.C. lines and, when required, storage of the resultant information, together with time of day and date over an extended period of time. The ammeter employs two C-shaped cores defining between two of the core arms a relatively large permanent gap that can pass the power line to facilitate mounting on the line using a live-line stick. One embodiment intended for mounting for an extended period of time also employs a clamp that can be manipulated using the stick to clamp it to the line and unclamp it, the clamp and core being related so that the power line passes through the center of the space between the cores. An embodiment intended for "spot" measurements has a locating member that performs the same function. A third device has the locating member in two parts that pivot to enable a large power conductor to pass through the slot in the locating member to the closed locating end thereof.