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a device for guiding a sower or planter to form interrows of a planned width. A marker consists of an extendable bar connected by a hinge to a sower or hitch. On the outer end of the bar is a disk, which is mounted at an angle and rotates freely; as it moves over the field, it leaves a furrow in the un-seeded area. On the next pass of the unit the furrow is used to guide the right front wheel or the inside edge of the right track of a tractor. Sowers and planters usually operate with right and left markers. The overlap (M) of the marker is determined according to the following formulas:
where a is the distance between the front wheels or the inside edges of the tracks, B is the distance between the extreme colters of the sower, and C is the size of the interrow.
an attachment to a single- or double-row sower that ensures parallel rows of seeds in subsequent passes. A marker consists of a beam with a weight on the end; the beam is secured to the front of the tractor. The tractor is steered so that the weight of the marker is above the track left by the planter wheel or marker disk on the preceding pass. Markers are often made reversible so that they can be used on both sides of the tractor.