KDevelop4/Manual/Tool list/Decoding table
The decoding table is an optional tool that is used only in pair with Hex Editor plugin, though it comes separately and is not affected by it.
To make use of that tool you need to open a document in hex editor that comes in hex editor plugin. The data you select with mouse pointer will be automatically put into the decoding table, though be careful because it does translate only the raw data and therefore the ASCII "1", for example, will be interpreted as decimal 49.