Tau tables (mean assumed = 0)
  n    0.01  0.025  0.05  0.10     0.90  0.95  0.975 0.99
============================================================
 25  -2.66  -2.26  -1.95 -1.61     0.92  1.33  1.70  2.16
 50  -2.62  -2.25  -1.95 -1.61     0.91  1.31  1.66  2.08
100  -2.60  -2.24  -1.95 -1.61     0.90  1.29  1.64  2.03
250  -2.58  -2.23  -1.95 -1.62     0.89  1.29  1.63  2.01
500  -2.58  -2.23  -1.95 -1.62     0.89  1.28  1.62  2.00
inf. -2.58  -2.23  -1.95 -1.62     0.89  1.28  1.62  2.00

                Tau tables (mean fitted in model)
  n    0.01  0.025  0.05  0.10     0.90  0.95  0.975 0.99
============================================================
 25  -3.75  -3.33  -3.00 -2.63    -0.37  0.00  0.34  0.72
 50  -3.58  -3.22  -2.93 -2.60    -0.40 -0.03  0.29  0.66
 100 -3.51  -3.17  -2.89 -2.58    -0.42 -0.05  0.26  0.63
 250 -3.46  -3.14  -2.88 -2.57    -0.42 -0.06  0.24  0.62
 500 -3.44  -3.13  -2.87 -2.57    -0.43 -0.07  0.24  0.61
 inf -3.43  -3.12  -2.86 -2.57    -0.44 -0.07  0.23  0.60

                Tau tables (trend fitted in model)
  n    0.01  0.025  0.05  0.10     0.90  0.95  0.975 0.99
============================================================
 25  -4.38  -3.95  -3.60 -3.24    -1.14 -0.80 -0.50 -0.15
 50  -4.15  -3.80  -3.50 -3.18    -1.19 -0.87 -0.58 -0.24
 100 -4.04  -3.73  -3.45 -3.15    -1.22 -0.90 -0.62 -0.28
 250 -3.99  -3.69  -3.43 -3.13    -1.23 -0.92 -0.64 -0.31
 500 -3.98  -3.68  -3.42 -3.13    -1.24 -0.93 -0.65 -0.32
 inf -3.96  -3.66  -3.41 -3.12    -1.25 -0.94 -0.66 -0.33


Example: Series seems to show a trend so you regress 
      Y(t)-Y(t-1) on 1, t, Y(t-1), Y(t-1)-Y(t-2)
with 100 observations.  Coefficient of Y(t-1) is -.0620 with 
standard error 0.2000.  Compare Tau = -0.620/0.2000 = -3.10 
to -3.41 and do not reject H0:unit root  at the 5% level. 
You could also use -3.45 arguing that this is more conservative
than the asymptotic value (the one justified by theory)