Private Equity - Gross IRR

I’m using the required readings and the calculation they have to get the gross IRR doesnt make sense to me. Pg 72 Book 5 of Required Readings. “Gross IRRs are estimated by calculating the IRR between the called down capital at the beg of period (col 1) and operating results (column 4)” The numbers they get on page 73 don’t correspond. For 2001 I’d take called down number (50) and subtract Operating results (-5). Instead the answer is -20. The only thing that gets their answer is taking the operatings results from 2001 (-5) and subtract it be the called down amount from 2002 (15). Which gets (20). Anyone solve this riddle?!?!?!?!?!?!?

What am I supposed to do here… figure it out for myself!!!

yes?!?!?!?!?