Many contractors have been using sets of basic equipment to evaluate subsoil conditions prior to bidding. Although this information is frequently furnished with contract documents and plans, wise contractors now frequently make their own analysis of the site by using hand or power tools, placing holes and borings and taking soil samples for their own analysis of the site. With a combination of accurate analysis and experience in handling various types of soil in construction, they can bid more intelligently on excavation and material handling, compaction and other problems concerned with maintaining the excavation in a dry condition or with maintaining the slopes during construction. The necessary equipment for this type of testing is low in cost and can be carried easily in the trunk of a car. There are kits available to take hand borings down to depths of approximately 25 feet. A small instrument, the pocket penetrometer, is frequently used to classify the materials taken in borings. This instrument is accurate enough to give a proper classification to cohesive types of materials and it is widely used by engineers and contractors for field evaluation of soil strengths. Of course, there are many other problems involved in the evaluation of soil and stability for construction purposes. The wise contractor knows when he is out of his depth and needs the services of a lab. Contractors have come to realize that concrete produced far in excess of the required strength and performance specifications can be as costly to them as concrete not meeting the specifications. Another low-cost instrument, the concrete air indicator, is widely used by contractors for a fast check of entrained air in concrete to make sure that the batch meets specifications. Many contractors use the more elaborate air meters of one-half or one-fourth cubic foot capacity for an accurate check once or twice a day to make sure they are in line with specifications.