Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online.Voltage is commonly used as a short name for electrical potential difference. Its corresponding SI unit is the volt (symbol: V, not italicized). Electric potential is a hypothetically measurable physical dimension, and is denoted by the algebraic variable V (italicized). The voltage between two (electron) positions "A" and "B", inside a solid electrical conductor (or inside two electrically-connected, solid electrical conductors), is denoted by (VA VB). This voltage is the electrical driving force that drives a conventional electric current in the direction A to B. Voltage can be directly measured by an "ideal voltmeter". Well-constructed, correctly used, real voltmeters approximate very well to ideal voltmeters. For non-scientists, an analogy involving the flow of water is sometimes helpful in understanding the concept of voltage (see below).