The simple formula for Return on Investment during a period---the one you probably know by heart---does not compute in the presence of cash flows (deposits or withdrawals) during the period. The author examined the modification by Joseph Dietz in 1966 to incorporate cash flows, but his approach is not exact. The more recent Time Weighted Return method circumvents cash flows exactly. Finally, the Internal Rate of Return method includes all cash flows and their dates. All methods can give different values and they do have different meanings. This book explains the equations behind all methods...