There isn’t a right or wrong unit of measurement to use. However, it is very important to stick to one system, using either all imperial measurements or all metric measurements for each piece of equipment on the farm. It makes sense to match other equipment to the harvester, as this would be the most difficult piece of machinery to try to adjust.

If the harvester has tyre centres based on imperial measurements, for example 120 inches, while this is close to 3 metres, it is actually 3.048m. Running another piece of machinery with metric 3m tyre centres over the same wheel tracks as a 120-inch harvester leaves little room for variation for autosteer systems. While the accuracy of many GPS systems may be 2 centimetres, it is likely that even this small variation

(3.000 versus 3.048m) will cause the autosteer system to work harder to maintain the correct line than it would otherwise have to if the tyre centres on the two pieces of equipment were matched.

While the position of the tyres within the wheel track is important for the function of the autosteer, the position of other implements and the tyres in relation to row spacing is also very important for minimising crop damage, compaction and maintaining the position of the nozzle in relation to the crop row. Generally, the narrower the row spacing, the more important the matching of equipment becomes, particularly for operators who plan on inter-row seeding, directed spraying or inter- row shielded spraying. Higher levels of precision introduce the opportunity for non-chemical control options as they become more readily available.