You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION 
     The present invention relates generally to roofing installations. More particularly, the present invention relates to a device for enabling a roofing installer to install sectional roofing sheets in an overlapping manner with uniform surface exposure. 
     BACKGROUND OF THE INVENTION 
     In the residential construction industry, roofing typically consists of layered water-shedding surface in the form of shingles. A shingle may be made from a variety of materials including, but not limited to, asphalt which is the dominant roofing material used in residential construction today. The asphalt roofing industry has existed since the late 1800&#39;s with improvements continuing to the present day. However, improvements in the asphalt roofing itself do not always translate into improvements in the installation of such asphalt roofing. Overall, such installation has remained unchanged for many decades or more. Often, those individuals in the roofing trade rely on verbal or visual information, rather than formal education or regular updates about changes in their profession. Thus, a roofing apprentice may be taught by an individual who has been doing something wrong or against manufacturer&#39;s recommendations for years such that mistakes are ignored or overlooked. 
     A byproduct of installing asphalt roofing shingles in a manner contrary to written, established roofing practices as outlined by manufacturers and roofing associations is that such asphalt roofs are susceptible to leaks or premature failure. The performance of asphalt roofing shingles is dependent upon several factors including, but not limited to, roof slope, ventilation, roof substrate, flashing and drip edges, along with the quality, placement, quantity, and installation of fasteners. Installation of fasteners is often done pneumatically and must be placed correctly. The location of the fasteners and relative placement of shingle to one another are basic to successful roofing installation. As each successive course of shingle is applied, it is offset from the course below. This offset is needed to adequately cover the butt joint of the course below. This butt joint is where water may leak into the living space below. Fastener locations are designed so that they receive the maximum protection from the course of shingles immediately above them. 
     Today&#39;s standard three tab shingle is common to many homeowners, however dimensional type (e.g., “raised tab”) asphalt shingles are becoming ever more popular. Some such shingles are designed to expose five inches of the shingle to the weather. In such shingle applications, manufacturers typically require fasteners be placed in specific locations along a line 5⅝ inches from the bottom (exposed) edge of the shingle. For high wind applications, even more fasteners are required. The difficulty to a roofing installer often becomes quickly and accurately fastening a loose shingle in the proper position atop a previous course of shingles with the appropriate amount of shingle exposure. Adding the vagaries of the work environment such as wind and rain compounds the difficulties experienced by a roofing installer. 
     It is, therefore, desirable to provide a mechanism for improved installation of roofing shingles. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to obviate or mitigate at least one disadvantage of previous roofing installation mechanisms. 
     In one aspect, the present invention provides a device for use in roofing installation, the device including: an inner portion having a first surface for engaging a first roofing shingle and a second surface for engaging a second roofing shingle; an outer portion movable relative to the inner portion and having a tab for engaging an end of the first roofing shingle; an adjustable portion affixed to the inner portion and having a stop edge for engaging an end of the second roofing shingle; and wherein the end of the first roofing shingle and the end of said second roofing shingle are separated by a distance corresponding to a predetermined surface exposure of said first roofing shingle. 
     Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the attached figures. 
         FIG. 1  is a perspective view of a roofing installation device in accordance with the present invention. 
         FIG. 2A  is a side view of the invention as shown in  FIG. 1 . 
         FIG. 2B  is a side view of the invention as shown in  FIG. 1 , but shown in compression mode with cross-sections of overlapping shingles engaged with the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Generally, the present invention provides an apparatus that enables a roofing installer to quickly and accurately install shingle-type roofing. The present invention allows a roofing installer to compensate for inconsistent spacing and nailing marks on shingles which may vary among manufacturers and among batches of shingles from the same manufacturer. The present invention also allows a roofing installer to accurately reduce shingle exposure necessary towards the ridge of a roof and thereby avoid unsightly final shingle spacing. As well, the present invention allows a roofing installer to significantly reduce reliance on chalk lines which are difficult to work with and impractical for use in wet weather. Although the present invention will be discussed in terms of shingles fabricated from asphalt, it should be understood that overlapping shingle-type roofing of any relatively thin sheet material (e.g., steel shingles) may benefit from the present invention. 
     With reference to  FIG. 1 , an embodiment of the present invention is shown in terms of a roofing installation device  100 . The device  100  includes three main parts: an inner portion  10 , an outer portion  20 , and an adjustable portion  30 . The inner and outer portions  10 ,  20  are shown as generally C-shaped brackets. However, it should be understood that the specific shape and configuration may vary without straying from the intended scope of the present invention. Indeed, a variety of shapes may be utilized as well as a variety of materials. Preferably, all elements shown are fabricated from a durable material such as, but not limited to, steel alloy. 
     The inner and outer portions  10 ,  20  are connected in a manner such that they are movable relative to one another. The manner of connection shown includes bolts  51 ,  52  which are tightened only enough so that travel through channel  20   a  is allowed when springs  41  and  42  are compressed. When compression of springs  41  and  42  ceases, it should be readily apparent that inner portion  10  is press-fit against tab  20   b  of the outer portion  20 . Such compression of springs  41  and  42  can be done manually by a user squeezing together the sections of inner portion  10  and outer portion  20  that surround the springs  41  and  42 . Although coil springs are shown, it should be understood that any similar mechanism may be used to maintain the inner portion  10  in the normal resting position against tab  20   b.    
     Still further, the adjustable portion  30  is shown affixed to inner portion  10  by way of wing nuts  61   a ,  62   a  and corresponding bolts  61   b ,  62   b  which can be loosened to allow sliding movement of adjustable portion  30  relative to inner portion  10  via channel  30   a . It should be understood that once positioned, the adjustable portion  30  is held stationary relative to the inner portion  10  by ensuring that the wing nuts  61   a ,  62   a  are fully tightened. Positioning of the adjustable portion  30  can therefore be varied by the user of the roofing installation device  100 . Varying such position accommodates differing shingle exposures as will be described further hereinbelow with further regard to  FIGS. 2A and 2B   
     Within each of the  FIGS. 1 ,  2 A, and  2 B, it can be further seen that the tab  20   b  of outer portion  20  includes a chamfered edge  20   c . The bevel that is formed on edge  20   c  allows the user to easily slide the tab  20   b  under a sheet of roofing when springs  41 ,  42  are manually compressed. Such configuration is shown in  FIG. 2B  where a bottom layer shingle  201  can be seen sandwiched between inner portion  10  and the tab  20   b  of outer portion  20 . In operation, this would be the first step whereby the bottom layer  201  of shingle would be laid upon by a top layer shingle  200 . The top layer shingle  200  would be abutted against the stop edge  30   b  formed on the adjustable portion  30 . 
     With further regard to  FIG. 2B , the adjustability of shingle exposure will be evident to one of ordinary skill in the art of roofing. Here, the distance between the end of shingle  200  abutting stop edge  30   b  and the end of shingle  201  at the tab  20   b  equates to the amount of top surface exposure of the bottom shingle  201 . Accordingly, from  FIG. 2B  it is readily apparent that a user may adjust the minimum top surface exposure of the bottom shingle  201  by loosening wing nuts  61   a  and  62   a  and sliding the adjustment portion  30  towards tab  20   b.    
     In  FIGS. 2A and 2B , bolts  51  and  52  are shown by dotted lines and are fixedly held within holes within the inner portion  10 , but loosely held within the channel  20   a  within the outer portion  20 . Lock nuts  51   a ,  51   b  and  52   a ,  52   b  secure the bolts  51  and  52  respectively in this manner. While a set of nuts (i.e., double-nuts) are shown for each bolt, it should be understood that any comparable locking nut such as, but not limited to, a nylon locking nut may be used to secure axial bolt movement, yet allow lateral sliding movement within channel  20   a  when springs  41  and  42  are compressed. 
     In operation, a user manually clamps the device  100  onto a previously laid row of shingles. Such clamping can be seen in  FIG. 2B  at tab  20   b . The surface exposure distance can be set either before or after clamping of the previously laid row of shingles. Moreover, the surface exposure distance may be incrementally varied while laying each subsequent layer of shingles. For example, when approaching the ridge of a roof the surface exposure distance may be reduced incrementally to avoid any unsightly transitions from a standard exposure to a much smaller exposure at the final course of shingle. Although not shown in the figures, it should be further apparent to one of ordinary skill in the art that the inner portion  10  may include measurement lines or notches to indicate incremental movements of the adjustment portion  30 . The inner portion  10  may also include further holes (not shown) to accommodate extreme movement of the adjustment portion  30  for very small surface exposures. In such instance, one or both bolts  61   b ,  62   b  would be moved to holes (not shown) closer to the tab  20   b  to allow the adjustment portion  30  to relocate towards the tab  20   b.    
     After the first two courses of shingle are laid to a drip edge and/or chalk line as is common in the roofing art, the following courses of shingle are advantageously installed using the device  100 . With further regard to operation of the device  100 , clamping force is applied by squeezing the device  100  with one hand, then engaging the edge  20   c  and tab  20   b  under the bottom edge of the bottom shingle. Depending upon factors such as whether the user is right-handed or left-handed and whether the user is laying shingle left to right or right to left, the device may be placed on either the left side or the right side of the shingle. Thereafter, the user lets go of the device  100  so as to allow the springs  41 ,  42  to provide the holding force to maintain the device  100  in place atop the bottom shingle. The user then has both hands free to move the top shingle into place with the surface exposure set as discussed above such that the top shingle rests against stop  30   b . As clearly shown in  FIG. 2B , the stop  30   b  is elongated perpendicular to the surface of the area of inner portion  10  upon which the shingle  200  rests. This effectively provides an L-shaped cross-section as shown in regard to the stop  30   b . As shown, the length of the stop  30   b  is several times the width of shingle  200 . Working, for example, from left to right, the device will be set in place at the left side to start a new course of shingles. The user will initially fasten the shingle on the left, disengage the device  100 , re-engage the device  100  on the right side, and add all remaining fasteners to secure the shingle as per manufacturers recommended fastener spacing. This is repeated until a complete course of shingle is made and then a new course may be completed. In this manner, the surface exposure can be quickly and accurately meted on each course and successive courses can include incrementally reduced surface exposure in an aesthetically pleasing manner. 
     The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.

Summary:
A roofing installation device for enabling quick and accurate installation of shingle type roofing. The device includes a generally c-shaped inner portion and correspondingly c-shaped outer portion slidable relative to one another. The inner and outer portions include at least one spring there between in an expansion state such that manual compression allows a user to clamp the device onto a first shingle layer. An adjustable portion is affixed to the inner portion and includes a stop edge to allow placement of a second shingle layer in such a manner to form a predetermined surface exposure of the first shingle layer. The predetermined surface exposure is variable by moving the adjustable portion relative to the inner portion. Such adjustment is accomplished in a quick, manual manner.