a contact bar code reader is suitable for reading 2 - dimensional bar codes . the reader comprises a housing having therein a source of illumination and optics for producing a diverging beam for illuminating a bar code symbol . a transparent frustoconical guide is removably attached to the housing , and has an conical angle corresponding to the beam &# 39 ; s angle of divergence . the guide is dimensioned to encompass the bar code symbol , and its line of contact with the data carrier is substantially fully visible to the operator , who can thus confirm that the guide is in proper operating position relative to the bar code symbol prior to initiating a reading operation . a reading operation can be initiated by pressing on the guide to actuate a switch , or on a manual trigger .