Zec 4:10 For who hath despised the day of small things? for they shall rejoice, and shall see the plummet in the hand of Zerubbabel with those seven; they are the eyes of YHVH, which run to and fro through the whole earth.

A "plummet" or "plumbline" in Scripture is the same device as a "plumb-bob" of today, functionally speaking.

16 ounce Swanson Brass plumb-bob hanging from 14.5 foot 8 lb. twisted #15 mason line.

To calibrate, I would think, to center the "chart" with a center point, on the day of the full moon, at sunset with the moon coming up in the east. Or at sunrise with the moon going down in the west.

Update: June 5, 2014:
I have checked the plumb-bob again, and it was left of the line.
I need a much higher point from which to hang the plumb-bob.

These two photo's taken with camera facing "South".  
Notice conjunction day (of the moon-SME event) plumb-bob is "east" of line. SunMoonEarth gravity. Notice day after conjunction plumb-bob is right back on the line.
May 28, 2014, 8:46 a.m.     East<----->West (day of conjunction) May 29, 2014, 10:36 a.m.     East<----->West (next day after conjunction)


Day of Conjunction-June 27, 2014- photos of plumb-bob: