A site providing promotion in search engines required a calculator to give the customer a price. Promotion in search engines is usually continuous. Initially, one should perform a large part of the work. Because of this, in addition to the monthly payment it was necessary to get prepay. This not very small prepay might scare away a client.
It was decided to give the customer an opportunity to reduce the prepay due to the nonlinear distribution of it in subsequent monthly payments. Calculator should give opportunity to choose amount of prepay.
There were also data fields for the customer's contact data so he could immediately send the selected payment option.