Excise sales invoice

we are new to making excise sales invoice in tally,so kindly help us with few queries on purchase: what is the RG23?can this number be kept blank??how is this column numbered in tally?is it item wise or as per excise invoice received date wise? on sales invoice:if my 50th invoice was a commercial invoice and my 51st invoice is the 1st excise sales invoice,then should the tax/retail invoice number column show 51 in excise sales invoice and excise invoice number 01? which options to select to do so in tally erp 9