RIVIERE CO DEC 14

2. If for example in the value at risk, (like in RIVIERE CO DEC 14) if the confidence level is 95%,answer have used 1.645. Then when do we use – 1.645 ? (the textbook that I have says that we use -1.645 because the value is below the mean therefore we use -1.65)
What is it mean by the” value is below the mean so we use -1.65 ????”