I used these along with the Junction Flashings while re-siding my large 3500 sq ft house with my wife and sons. We are (or were) not pros but the city inspector told us we did a better job then locally approved contractors. You only need to set the first row well leveled and this allow to build on top with very little adjustments. The only reason there may be 1mm adjustment requirement once in a while is because James Hardy are not consistent in width. Once the first row is installed, one person can keep working on following rows and even do small adjustment by one self since the planks are already leveled and may only need to raise by 1mm with one hand on one end to compensate for planks inconsistency. 95% of the time there is no need for compensation at all. Could not have made it without these. We used a few boxes fort he entire house.