This Battery was part of Pegram’s Battalion served as a member of the Artillery Reserve in the Third Corps, Army of Northern Virginia. The Battalion commander, Major William Ransom Johnson Pegram (June 29, 1841 – April 2, 1865) was an important young artillery officer in Robert E. Lee’s Confederate Army of Northern Virginia during the American Civil War. He was mortally wounded in the Battle of Five Forks. He was the younger brother of Confederate General John Pegram, who was also killed in action. His grandfather, John Pegram, was a major general during the War of 1812. This battery (the subject of this waymark) however, was commanded by Captain Joseph McGraw. McGraw was a Teamster from Sharpsburg, Maryland. He was wounded in Seven Days and lost his arm at Spotsylvania. He rose to battalion commander. McGraw lived in Brooklyn, New York after war. There is hardly any trace or record of the man on the net.
The McGraw's Purcell Artillery - CS Battery Marker and cannon are southwest of Gettysburg, on the left or east side of West Confederate Avenue if traveling south. This part of Confederate Avenue is located at McMillan Woods. The Thomas's Brigade tablet is directly across the road. 
Visitors can park on the side of the road at intermittent cutouts; there is a cutout located here. When visiting this and other monumentation and tablets, avoid parking on anything green or you will be ticketed by the park police. They almost got me. I visited this monument on Saturday, March 10, 2012 at approximately 12:36 PM, just before the clocks were set ahead for the Spring. I was at 582 feet ASL elevation.
These monuments were first built in 1900 and concluded in 1906 according to the NRHP nomination form. Some sites have the monuments being erected in 1910 or later. 1910 seems to be the most reasonable date so we will go with that. It is amazing with all the work and effort exerted to make the Gettysburg National Military Park a reality, no one took the time to keep accurate records and correct installation dates. The work was done under the direction of the Gettysburg National Park Commission (established by the United States Department of War), after they took over the administration of the park from the Gettysburg Battlefield Memorial Association (whose funds had expired) on March 3, 1893, and whose stewardship was then transferred to the National Park Service in 1933 SOURCE.
Draw the Sword, with descriptive help from the NPS site, offers the following description: Cast iron tablet, 3’8" x 3’4", with raised inscription painted in a contrasting color and mounted on fluted cast iron post. All 4’4" H. Tablets casts by Calvin Gilbert. The inscription on the 3.8' x 3.4' tablet narrates the events associated with Battery during the Battle. The inscription on the monument reads:
Army of Northern Virginia
Hill's Corps Artillery Reserve
Pegram's Battalion McGraw's Battery
The Purcell Artillery
Four Napoleons
July 1 In position south of the Chambersburg pike on the ridge west of Herr's Tavern and actively engaged.
July 2 Early in the morning occupied this position and took part in the day's conflict with the Union batteries and now an then dropped a shell among the busy sharpshooters.
July 3 Remained here and actively participated in all the operations of the artillery.
July 4 Withdrew about sunset and began the march to Hagerstown.
Losses not reported in detail.
There are hundreds of non-sculpted monumentation for the various Confederate States & Union units which fought at Gettysburg, about 10 different variations of tablets, markers and monoliths by my reckoning. Six designs represent brigade (2), division (2), corps (2), & army headquarters (2), each different in a subtle way so as to distinguish between armies. Battery/advance position markers and regimental monuments for United States Regulars & Confederate have their own distinct design (2), bringing the total to ten deigns at the battlefield. Many of the tablets were created by Albert Russell & Sons Co. of Newburyport, Massachusetts and are made of granite, bronze and concrete or like this one, cast iron. All of these tablets were designed by architect Colonel Emmor Bradley Cope (July 23, 1834 - May 28, 1927). He designed pretty much every tablet for both the Union and Confederate armies, each one distinct, with several different varieties. He is buried in Evergreen Cemetery 
in Gettysburg, as well as he should be as this park and most of the things seen here today were designed by him and as such, are his legacy. These monuments/tablets were erected just after the turn of the century during the first and beginning of the second decade of the 20th century. Each one has since been preserved or restored at least twice since the turn of the 21st century. The plaques and tablets were erected by the Gettysburg Park Commission (established by the War Department). The Gettysburg Park Commission is also referred to as the Gettysburg National Military Park Commission or the Gettysburg National Park Commission, to clear up any confusions, especially my own.
On October 1, 1898, the Gettysburg National Park Commission in a letter to the Secretary of War set gave recommendations for continuing the task of organizing and progressing the work of the Gettysburg National Military Park. Every November they wrote their annual report which outlined the work of the GNPC for that year. The following is an excerpt from that report relevant to this waymark. The link at the end of the paragraph will take you to the entire report. The method of marking the positions of troops on this field, as approved by the War Department, is to place the principal tablet or monument of each command at the position occupied by the command in the main line of battle, and to mark the several important positions subsequently reached by each command in the course of the battle by subordinate and ancillary tablets, with appropriate brief inscriptions giving interesting details and occurrences and noting the day and hour as nearly as possible. SOURCE
Most of the Commission reports have been digitized and can be found HERE. The initial 1893 report up to and including 1921 can be found here. 1922 to 1926 are missing and have yet to be discovered. The years 1927 to 1933 were discovered in 1996 and are also included. To my knowledge this is the most comprehensive list of documents that illustrated the development and formation of the park.
Information about these specific types of monuments:
CONFEDERATE BATTERY AND BRIGADE TABLETS (ADVANCED POSITION)
These tablets are 3’8" x 3’4" in dimensions, with carefully prepared inscriptions cast in raised letters painted in white (contrasting the black background) describing the part taken in the battle by each brigade, their position and stating its numbers and losses so far as practicable to obtain. They are mounted on iron pillars or fluted cast iron posts about 3 feet high, grouted in the ground, and the tablets are inclined at a suitable angle so that the inscriptions can easily be read by persons riding or driving on the avenue. Every tablet is 4’4" in height. The advance position markers were cast by Calvin Gilbert. SOURCE & SOURCE. These tablets usually have accompanying artillery pieces which flank the tablet on either side. There can be as little as one cannon and as many as four. The cannons usually represent the battery and the armaments that specific battery used at Gettysburg. The cannons presumably point in the same direction as they once fired at the enemy in 1863. Sometimes only the cannon pads are present as the guns are periodically removed for service, cleaning, restoration, maintenance, etc.
The McGraw's Purcell Artillery - CS Battery Marker is a contributing feature to the Gettysburg National Military Park Historic District which is nationally significant under NR Criteria A, B, C & D. Areas of Significance: Military, Politics/Government, Landscape Architecture, Conservation, Archeology-Historic. Period of Significance: 1863-1938. The original National Register Nomination was approved by the Keeper March 19, 1975. An update to this nomination was approved by the Keeper on January 23, 2004. The monument is identified as structure number MN628-D.
From the Nomination Form:
Civil War tablet that marks position of McGraw's CS Battery on July 2-4, 1863. Narrates events associated w/ Battery during Battle of Gettysburg.
Short Physical Description:
MN & 4 Cannons. Cast iron tablet, 3'8" x 3'4", with raised inscription painted in a contrasting color and mounted on fluted cast iron post. All 4'4" H.Cast by C. Gilbert. 2 cannons on N/S sides of tablet.
Long Physical Description:
Located on E side of West Confederate Avenue at McMillan Woods. Cannons have been removed from this site, cannon pads remain.
My Sources
1.
NRHP Nomination Form
2.
Stone Sentinels
3.
Virtual Gettysburg
4.
Draw the Sword
5.
Historical Marker Database
6.
Wikipedia