You can access the Hydrometer Correction tool under the menu. This tool is useful for converting your actual hydrometer readings to the correct value. Enter in the temperature at which you took the sample, the temperature at which the hydrometer is calibrated (typically 60° or 68° Fahrenheit), and the actual hydrometer reading. The corrected reading will be calculated.
The data that QBrew uses is in the file qbrewdata, typically installed under /usr/local/share/qbrew under Unix, or in the install directory under Windows.
If there exists a file in the user's home directory with the name of .qbrewdata, then this file will be used instead. It is simple to add new ingredients, or modify the values for existing ingredients. Simply copy over the main qbrewdata file to the user's home directory, rename it to .qbrewdata, then edit it with any text editor. The file format is in XML and should be self explanatory.
There is no clear concept of a home directory under Windows. Users of that OS can safely ignore the preceeding paragraph, content in the knowledge that ignorance is bliss.
US units of measurement are used by default in QBrew. This can be changed in the configuration dialog. Both US and Metric measurements are available.
Please note that converted from one system to another and back may result in round-off errors during the conversion.
QBrew has many command line options. If you type qbrew -help in a terminal, you will get a list of all available command line options for QBrew. Probably the most useful is to pass the name of a recipe to qbrew, as in the following example: qbrew mybestale.qbrew.