120 A MANUAL FOR NORTHERN WOODSMEN 
3. After the boundaries are surveyed and the primary 
point in elevation is fixed, a topographic survey and timber 
estimate might be made together by means of the strip 
system of survey described on page 188. For the topo¬ 
graphic work, a barometer would be carried in the party 
and the elevation of needed points read and noted or 
plotted down in connection with the chainage by the note- 
keeper. If the air pressure was not steady, it would be 
necessary for the barometer man once in a while to leave 
the party and go back to the base for correction. The 
combination of barometer and barograph gives rise, in a 
