Nettle Hill of June 29 closely matches Stanton Bridge of July 4 in astronomical meaning 

One of the most important clues to interpreting Nettle Hill of June 29 is that its "1st thin circle" surrounding a "central Sun" has been drawn slightly off-centre, in order to represent the highly elliptical orbit of planet Mercury. Hence its "2nd thin circle" may be assigned to planet Venus. Those crop artists also used a clever form of field symbolism to make the same point: nearby we can see a tall tree with circular tramlines around it, to represent "Venus in orbit about our Sun".  

As of June 2008, three full orbital cycles of Venus (large white numbers) remain until the end of our current Mayan Sun-Venus calendar in March 2013. Any full synodic cycle of Venus takes 584 days or 1.6 years, hence there will be 3 x 1.6 = 4.8 years until March 2013.  

Likewise, five half-orbital cycles of Venus (small blue numbers) remain until Venus transits the face of our Sun in June 2012. Any half synodic cycle of Venus takes 292 days or 0.8 years, hence there will be 5 x 0.8 = 4.0 years until transit on June 6, 2012.  

This is the same 52 or 104-year calendar that the Olmecs, Mayans or Aztecs used long ago in central America (see HERE  or HERE). Five days later at Stanton Bridge on July 4, the Mayan number "three" appeared, once again to remind us apparently that only three full orbital cycles of Venus remain until their calendar ends on March 28, 2013.