Accurate calibration of the harvester head relies on accurate manual log measurements.If you are consistently producing out of specification logs with your harvester, even after calibration, it could be because the manual log measurements being carried out as part of the calibration process are incorrect. In a study by Martin Strandgard in the International Journal of Forest Engineering (Volume 20, No. 2 July 2009), it was found that there was variation in manual length measurements depending on where the length measurement was taken, mainly due to non-square log ends. When using log callipers it was also possible to read incorrect log diameters with eccentric logs, if only one diameter reading was taken. It is therefore clear that incorrect readings can be taken, which could then be used to calibrate the harvester.
In order to ensure that the manual measurements are carried out correctly, the length measurement should be taken on the same side of the log as the harvester would measure it. Diameter measurements should be taken with a diameter tape to reduce the effect of eccentricity. It is also best to select logs for calibration that are uniform in shape. This eliminates possible sources of error.
For a more complete account of the research, please access the journal article at http://www.lib.unb.ca/Texts/JFE/