570 Subsurface Geologic Methods 



features of both the regular and small machines have been preserved. 

 Complete redesign indicated by field experience has been done on all parts 

 of the instrument. Through this redesign a machine will be produced which 

 will be easier and cheaper to manufacture and maintain. The instrument 

 will contain fewer and simpler parts which to the operator means longer 

 and more trouble-free operation. 



The type "A" single-shot instrument will be 1^ inches in diameter, 

 but will use a disc 1^^ inches in size. This disc should be easier to read. 



A telltale device on the slug-trap operating lever will indicate whether 

 a disc is loaded in the machine or not. A larger sylphon and a more sensa- 

 tive shock-mounted compass needle in the angle unit will better provide 

 for high-temperature surveys and make the readings more accurate. Newly 

 designed loaders and unloaders are being manufactured for this modern 

 instrument. 



It is probable that in time the type "A" instrument will displace both 

 the regular and small single-shot machines now in use. 



Multiple-shot surveying instruments, as the name implies, are capable 

 of making a number of readings in one run. They are used principally to 

 survey wells that were drilled and put on production before the importance 

 of surveying was generally accepted, to learn the course of a well after 

 casing has been set, or to locate the course of a well on which a drift indi- 

 cator has been used during drilling. Multiple-shot machines generally 

 effecting a saving in rig time over the single-shot method by surveying 

 both cased and uncased wells of any depth drilled to date in a single run. 

 However, the information usually is obtained too late to change the course 

 of the well without plugging and sidetracking the original hole. Photo- 

 graphic means for recording data are used in modern multiple-shot ma- 

 chines. 



The Eastman DX-type multiple-shot machine is illustrated in figure 

 291. A small motor, powered by batteries in the machine and controlled 

 by a main switch, runs throughout the survey. This motor turns a gear 

 train, which alternately lights the bulbs for an exposure interval of six 

 seconds, and moves the special 16-mm. recording film ahead. Film is 

 metered from the new film spool to the takeup spool over a sprocket wheel. 

 The lights illuminate an angle unit almost identical with that used on the 

 regular single shot. A camera lens focuses the image of the angle unit 

 on the film. Simultaneously, the face of a timing clock is photographed 

 on the film as a reference. Enough heat-resistant film is spooled in the 

 film box to enable the machine to take records for 17 hours at 90-second 

 intervals. The angle unit has an off-center, tapered groove cut in its 

 bottom so that it will fit into the barrel in exactly the same position each 

 time. An orienting lug, exactly parallel to the groove, is located in the 

 angle unit where it is photographed. The upper end of the machine is 

 fitted with an expansion head so that the instrument may be tightly 

 clamped in the barrel. 



