Assessment of variability of yield is the main step for precision farming management. It is necessary to know the accurate information and assessing accurate quantity for main reasons of variability of crop production. Site specific nutrient, water, weed management and yield variability assessment are the major component of site specific precision agriculture. A yield monitor was continuously used for two years  assessing yield variability and generating site specific maps in what crop for precision agriculture. Yield monitor collects and saves grain flow, grain moisture, area covered and geographic reference of place and also shows yield variability. Main components of yield monitor are GPS receiver, yield sensor, moisture sensor, data collector, task computer and a console which is installed in combine harvester. The average yields of wheat grain were 4438.1 and 3582.8 kg/ha in the year 2013 and 2014 respectively. The average standard deviation (SD) of yield was 1422.2 and 1009.6 kg/ha with coefficient of variation (CV) of 0.33 and 0.28 in 2013 and 2014 respectively. The yield data                 collected from yield monitor shows the variability in field.