The storage monitor is a basic part of the ME network. By clicking on it with an item, you may see how many of that item is currently in that network in real-time. The block automatically updates every time the item is added or removed, so - for example - you may know how much iron ore is in your network by placing a monitor next to a furnace and setting it to show the ore. Useful for working out the kinks in machine chains. The monitor needs to be connected to the network with an ME cable or by being placed next to a machine already connected to the network.
In addition, a conversion matrix may be used to upgrade the monitor by shift + right-clicking the monitor. This will allow you to take full stacks of items from the network by right-clicking a locked, upgraded monitor.To lock and unlock a monitor, simply shift + right-click it with a wrench such as the prototype omniwrench. This locks the item on the monitor and keeps it from being replaced, and with upgraded machines grants the ability to right-click the machine and take up to a full stack of that item from the network.