The values in right columns can be of only two types: true or false. These values cannot be attributed to either of the types considered above since they are not numbers at all. They are not the values of color, taste, amount and so on, either. However, they bear an important sense. In MQL4, such values are named Boolean, or logical, values. Constants and variables of bool type can take only one of two possible values: true (True, TRUE, 1) or false (False, FALSE, 0). The values of constants and variables of bool type take 4 bytes in the computer memory.