ABSTRACT
This chapter describes some of the calculational and technical details so that non-practitioners feel able to make an informed judgement about lattice calculations, and see where progress will be made in the future. Lattice quantum chromo-dynamics (QCD) was invented, way ahead of its time, in 1974. It really became a useful technique in the 1990s when a huge amount of progress was made in the understanding and reduction of systematic errors. To discretise gauge theories such as QCD onto a lattice requires a little additional thought because of the paramount importance of local gauge invariance. The inclusion of quarks in the lattice QCD action causes several difficulties related to their fermionic nature and makes lattice QCD calculations very costly in computer time. Non-relativistic version of QCD (NRQCD) is an effective theory, containing the right physics for low momentum heavy quarks. The spectrum of heavy-heavy states has largely been the province of NRQCD.
