Validation (or testing) is a painstaking procedure but an essential part of the total quality assurance process. It is the study of the effectiveness of design prototypes, acknowledging any weaknesses encountered. The purpose of validation is to check to see if the program meets its specified objectives. Realising the objectives of the validation process requires clear testing procedures to be devised. In-house debugging is the testing of a program's functionality: do all the buttons and effects operate as intended without causing the system to crash? It will also cover performance testing under different hardware and operating system configurations. Trialling refers to testing the program's end-user objectives in a simulated or real end-user environment -- field testing. The process of testing, trialling and revision is cyclical. Program revision sends the team back to the debugging process and on to field testing again. One of the big problems in the process is that exhaustive testing is usually impossible, given the limited time and resources available for the project's lifetime and the pressures to demonstrate working models to clients prematurely.