.Modelica.Blocks.Sources.RealExpression .Modelica.Blocks.Sources.RealExpressionThe (time varying) Real output signal of this block can be defined in its parameter menu via variable y. The purpose is to support the easy definition of Real expressions in a block diagram. For example, in the y-menu the definition "if time < 1 then 0 else 1" can be given in order to define that the output signal is one, if time ≥ 1 and otherwise it is zero. Note, that "time" is a built-in variable that is always accessible and represents the "model time" and that variable y is both a variable and a connector.