Window Size Specify the distance to add to both ends of Start and End variables. Example: A Window Size of 100 given a gene size of 10 results in a total of 210 bases shown in the browser: 100 bases upstream of the gene of interest, and 100 bases downstream of the gene of interest. To Specify Window Size: Check the Set window size box to activate the Window Size field. Type a value, between -1000000 and 1000000, into the Window Size field.