You can make a spot-on call by pressing . When making a spot-on call, you are saying that the last bet made by the previous player is 100% correct. If that person says that there are 4 5s on the table, (and its correct) you can make a spot-on call. If correct, everyone will lose a die. The achievement should unlock immediately after the play is pronounced correct.
This is best done in a Private match. Two players is most recommended, as the less amount of players, the less amount of die on the table. So, check out the Achievement Trading Thread for partners.