Described are techniques used in a computer system for handling data operations to storage devices. The object will be attained by following process: mouse genomic libraries are screened with rat NaG cDNA as a probe, then Nav2 gene of genomic DNA is isolated, and a targeting vector is constructed by inserting marker gene such as neo gene into the exon of Nav2. The device is preferably sized to be hand-held in one hand and operable with one hand.