To ensure that thinning is done properly and correct due to instruction, regularly manual monitoring of the stand is done by the harvester operator after thinning. The aim of this study is to investigate the reliability of a newly developed program, that is using harvester data to automaticly calculate stand variables after thinning. A manual forest inventory was carried out in ten differens stands i south west of Sweden, where basal area, stem density, volume and species mix were estimated and compared to the automatically calculated data. The results shows that volume and stem density were estimated with high precision while the systematic deviation for basal area was 10 %, which is a significant differens.