A description of the original code LAWAL was published in the journal "Particle Accelerators" vol.1, pp.311-326 (1970), while LAWAT was already described in CERN report 69-15. Originally, Bruno Zotter wrote his own subroutines to calculate modified Bessel functions of complex argument. He rewrote both codes in the 1980ies using MATHEMATICA, which provided these functions. Subsequentially, Olav Meincke and Eberhard Keil used them to estimate the impedances of the SPS and the proposed VLHC (EPAC 1998), Eberhard modified the codes by combining recurrent parts into "packages".