Should the formula for test statistic have an absolute value? I have been given a formula for calculating a t test statistic as 
$$t_{n-1} = \frac{ \bar{x}- \mu_0}{\frac{S}{\sqrt{n}}} $$
Where $\bar{x}$ is the sample mean, $\mu_0$ is the hypothetical true mean, $S$ is the sample standard deviation and $n$ is the sample count.
But when I plug my values in, the outcome is negative.
I don't see how to look up a negative value on the T-table.
Should I be taking the absolute value?

In a previous question you were looking at 
and wanted the column labelled cum.prob $t_{.975}$ or one-tail $0.025$ or two-tails $0.05$
If the table had been extended to the left, then by the symmetry of the $t$ distribution,

*

*there would have been a column labelled cum.prob $t_{.025}$ or one-tail $0.025$ or two-tails $0.05$

*and it would have had the values $-12.71, -4.303,-3.182,\ldots$
and similarly with the other columns.
Doing this would double the size of the table without adding useful information beyond the change of signs.
