Section 4 of the Negotiable Instruments Act 1881 defines: "A "Promissory Note" is an instrument in writing (not being a bank note or a currency note) containing in unconditional undertaking, signed by the maker, to pay a certain sum of money only, to or to the order of, a certain per-son, or to the bearer of the instrument." As can be seen from the various legal decisions, the primary requisites and the proper tests to determine the validity of an instrument as a promissory note are well settled. (See Bahadurrinisa v. Vasudeva, AIR 1967 Andh Pra 123; Jagjivandas v. Gumanbhai, AIR 1967 Guj 1; Firm Chunnilal Tukkimal v. Firm Mukat Lal Ram Chandra, AIR 1968 All 164: Rama-chandraiah v. Firm Gandham Narayana Gupta, AIR 1968 Andh Pra 325; State Bank of Hyderabad v. Ranganath Rathi, AIR 1966 Andh Pra 215). The actual words used in a promissory note are of so much importance that they should conform to the definition under this section and should not be ambiguous ....