Media scheduling involves determining (1) when to advertise, (2) how much advertising space or time to purchase each time, and (3) how frequently to advertise the message across different media over a period of time. There are several models for scheduling including continuity, flighting, and pulsing. Continuity involves steady advertising with little variation over the campaign period. Flighting uses intermittent periods of advertising alternating with shorter periods of no advertising. Pulsing combines flighting and continuity with a low level of advertising all year and heavier advertising during peak selling periods. Macro-scheduling allocates expenditure and frequency in relation to seasons or business cycles while micro-scheduling allocates expenditure and frequency within a short period to maximize response.