How to understand the quantity available in supply and demand inquiry form


Hi, I'd like to know if there is anyone could help to explain how the quantity available on 2018-2-28 and 2018-3-1 is calculated and popped in S&D interactive program? Thank you.
I can see on 2018-2-28 there is a shipment of sales order occurred in system. However, the line of date 2018-2-18 is 170. while 2018-3-1 is 40, strange. also this 40 goes to 3-5 and 3-31.
170 is the DF(demand forecast) entered for 2018-3-1.