Similarly, only in the tool dialog box can Raster Calculator variables be contained within percent signs ( %) or quotation marks ( "). When working in Python itself, layers must first be cast as Raster objects. Only in the Raster Calculator tool dialog box can layer names be used directly with operators. Since there is a specific output parameter in the Raster Calculator tool dialog box, Map Algebra expressions do not include an output name and an equals sign ( =) when using the Raster Calculator. While Map Algebra is used both in the Raster Calculator and directly in Python, there are some differences in the syntax that you should be aware of. Example expressions in the Raster Calculator tool dialog box For more information, refer to the usage tips listed in the Raster Calculator tool help. When multiple Relational or Boolean operators are used in a sequence, the expression requires parentheses. For example, to use the IsNull tool, be sure to type it as IsNull, instead of Isnull or isnull. Since the expression entered in the Raster Calculator tool will be executed in Python, and Python is case sensitive, it is important to use the correct capitalization of the tool name. 
When building expressions in the Raster Calculator tool, clicking and double-clicking on the various layers, variables, buttons, and tool names available in the dialog box will help you to avoid syntax errors that may otherwise be made while typing.
An example Raster Calculator expression in ModelBuilder.Example expressions in the Raster Calculator tool dialog box.
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