Select from Table 4, 18 additional PU's, using a random number following 
the last one taken. Recalculate s, S and y, from the final number 
after enumeration of the SU's (plots) in the field. If s from 10 PU's 
was calculated to be > 27 per cent, m would be > 30. Then only 30 
would be taken first and calculation of s made from it, in order to 
avoid needlessly exceeding the number of PU's which is required in the 
sample. 
References 
M.H. Hansen, W.N. Hurwitz, Sample Survey Methods and Theory, 
W.G. Madow Volume I, Methods and Application, 
1953 638 pp. 
F. Loetsch, F. Zóhrer and Forest Inventory, Volume II, 469 pp. 
K.E. Haller 
1973