to i send to the other party now"; the other is "how much will i get back later".
you set one direction to be a "positive" cash flow; the other direction needs to be "negative".
so the sign is just an indication of which direction the money is going.
is the use of the calculator for this problem just a creative approach? how does the context of cash flow fit into the problem?
i get a payment of 121 from a bank immediately, and 121 a year later, am i then giving 144 back to the bank at end of year two and three? if so why? 