TIMBER ESTIMATING. 75 
The systematic gridironing of a tract, however, would not always 
be the best plan of distributing the strip surveys. Thus, for 
example, in mountain country, where the merchantable timber is 
on certain types of land or slope or in small or very irregular-shaped 
stands, it is usually better to lay off strip surveys more or less 
irregularly, in such a way as to obtain an average yield per acre of 
the type or area under immediate examination. If the timber 
on a smail watershed is to be estimated and the yield per acre 
along the stream differs materially from that on the slopes, strip 
surveys must be taken, and the yield per acre determined sepa- 
rately, for each type of forest. The strips are laid off by judgment 
and not by rule, as in the gridiron method. 
In mountainous country the most exact results come from run- 
ning the strips as far as possible directly up and down the slopes, to 
cross the different types. Only in this way can a fair average be 
obtained. Strips run along the bottom of deep coves or ravines to 
get the average stand in such coves, will in reality measure the very 
best timber and the result may be an overestimate of the actual 
stand by 100 per cent. To separately mark the type areas, the 
strips need not be confined to the type, but, in continuing through 
successive types the boundaries between types will be noted and 
separate tally sheets or portions of sheets used for the different 
types. The area of each type afterwards may be sketched in a 
map as shown by the intersections of the strips; or the proportion 
of each type in the strips may be taken to correctly represent that 
for the whole tract. 
MEASUREMENT OF THE TREES. 
The strip methods may be used without calipering the trees, 
but by counting them, or by guessing the contents of each mer- 
chantable tree as it is counted. Usually, however, the trees are 
calipered to the nearest inch at breastheight. Sometimes the 
trees are grouped into diameter classes of 2 or more inches. Ordi- 
narily one measurement of each tree is taken unless it is obviously 
eccentric, when two diameters at right angles are measured, and 
the average is recorded as the diameter. Care must be exer- 
cised not to take the measurements below breastheight. A 
tired man is apt to lower his calipers and measure at 3 or 34 feet 
