▁high - level ▁tournament s , ▁where ▁screens ▁are ▁used , ▁the ▁procedure ▁is ▁to ▁ask ▁the ▁screen - mate ▁about ▁their ▁calls ▁as ▁well ▁as ▁their ▁partner ' s ▁calls . ▁In ▁serious ▁online ▁tournament s , ▁the ▁procedure ▁is ▁for ▁the ▁player ▁making ▁the ▁call ▁to ▁self - alert ▁it , ▁but ▁the ▁explanation ▁is ▁visible ▁only ▁to ▁the ▁oppon ents . ▁ ▁Classification ▁ ▁B idd ing ▁systems ▁can ▁be ▁class ified ▁into ▁two ▁broad ▁categories : ▁natural ▁systems ▁and ▁artificial ▁systems . ▁In ▁natural ▁systems , ▁most ▁b ids ▁( es pecially ▁in ▁the ▁early ▁phase ▁of ▁the ▁b idd ing ) ▁denote ▁length ▁in ▁the ▁suit ▁bid . ▁In ▁artificial ▁systems , ▁the ▁b ids ▁are ▁more ▁highly ▁cod ified , ▁so ▁that ▁for ▁example ▁a ▁bid ▁of ▁ 1 ▁may ▁not ▁be ▁related ▁to ▁a ▁holding ▁in ▁the ▁club ▁suit . ▁ ▁Natural ▁system ( s ) ▁are ▁the ▁" ling ua ▁fran ca " ▁of ▁bridge ▁players , ▁with ▁regional ▁variations . ▁Thus , ▁a ▁new ▁partners hip ▁can ▁agree ▁to ▁play ▁a ▁natural ▁system ▁and ▁understand ▁each ▁other ▁fairly ▁well . ▁Play ers ▁sometimes ▁alter ▁certain ▁aspects ▁of ▁a ▁system , ▁adding ▁their ▁specific ▁agre ements ▁or ▁preferred ▁convent ions . ▁ ▁Str ucture ▁and ▁meaning ▁of ▁opening ▁b ids ▁are ▁the ▁common ▁determ ining ▁factor ▁for ▁system ▁classification : ▁in ▁most ▁modern ▁natural ▁systems , ▁opening ▁b ids ▁of ▁ 1 ▁through ▁ 2 ▁have ▁the ▁same ▁or ▁similar ▁meaning , ▁with ▁level -