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Optimisation issues The time taken to process events grows with the multiplicity $n$ of the input objects as $n^3$. As the multiplicity grows with energy, and current and future colliders have ever higher event rates, timing issues are therefore of increasing practical importance. A few compilation options are worth considering if speed is critical. A compile option to switch from single to double precision arithmetic is available, but single precision is used by default as this increases the speed by around 10%. In gcc, the option -O2 is essential; higher or lower optimisation levels seriously degrade performance. Choice of architecture is also important. For example using the gcc compiler flag -march=athlon on an Athlon processor gives a performance gain of around 5%. More details on performance issues are given at http://www.ktjet.org/.