They also receive income through small-scale personal contributions. The nature of GISCC's revenue model focuses primarily on the sale of donated goods in its retail stores, which has the effect of producing a very predictable source of revenue for the organization. They experience sales fluctuations during the holiday season; Revenues are highest in the fall and lowest in the summer months. Furthermore, personal contributions are very incidental and constitute between 1 and 2% of their budget in an average year (S. Chalupa, personal communication, October 14, 2015). This is not significant enough to cause drastic fluctuations in their revenue stream. According to Sheryl, GISCC has no significant fluctuations in revenue (personal communication, October 14,