Average delay is calculated by determining Workload(Calls per Interval*AHT per Interval/1800 or 3600 (depending on halh-hour or hour staffing targets) and target online agents, Based on the arrival times and true position staff a percentage of calls may not be answered immediately. The percentage of calls delayed(delayed calls/Total calls) * the avg delay = the average delay of all calls. Your target ASA on the calculator is based on the same principal. Actually, Avg delay is a incorrect term because a percentage of calls do not receive any delay, therefore average speed of answer may be a better term.
I hope this helps.