IFRS 2 Share based payments

Hi,

I am trying to work out June 2015, Q 2(C) and the following is the info provided;

on 1/05/2012 co granted 500 SAR
Rights vested on 30/04/2014
rights can be exercised from 1/05/2014 – 30/04/2016
FV of SAR at 30/04/2013 $9

when working out the liability the examiner weorked it out as follows;

285 Managers x 500 sh x $9 x 1/2

i cannot understand why the examiner included the 1/2…….

Thanks