[en] Program PICKER is a data-selection program for the geochemical code PHREEQE. It enables the PHREEQE code to be used in conjunction with a fully documented master database, such as the Nirex HATCHES database without the need to amend the program to store unnecessarily large amounts of data. The program PICKER performs data selection prior to each run, or set of runs, using the program PHREEQE. The user supplies a list of the elements to be included in a particular series of calculations, and the program scans the large database and selects all the possible species and minerals which the elements may form. These data are then converted into the format required by the original, verified PHREEQE code. No other selection criteria such as data quality or kinetic constraints are introduced. Thus use of the PICKER code for data selection does not bias the calculation in any way. The method combines the versatility of a large thermodynamic database with the efficiency of the original, well-verified PHREEQE code. (author)