convention is that the flavour charge and the electric charge of a quark have the same sign. Thus any flavour carried by a charged meson has the same sign as its charge. Quarks have the following flavour quantum numbers: The third component of isospin (usually just "isospin") (), which has value for the up quark and for the down quark. Strangeness (): Defined as where represents the number of strange quarks () and represents the number of strange antiquarks (). This quantum number was introduced by Murray Gell-Mann. This definition gives the strange quark a strangeness of −1 for the above-mentioned reason. Charm (): Defined as where represents the number of charm quarks () and represents the number of charm antiquarks. The charm quark's value is +1. Bottomness (or beauty) (): Defined as where represents the number of bottom quarks () and represents the number of bottom antiquarks. Topness (or truth) (): Defined as where represents the number of top quarks () and represents the number of top antiquarks. However, because of the extremely short half-life of the top quark (predicted lifetime of only ), by the time it can interact strongly it has already decayed to another flavour of quark (usually to a bottom quark). For that reason the top quark doesn't hadronize, that is it never forms any meson or baryon. These five quantum numbers, together with baryon number (which is not a flavour quantum number), completely specify numbers of all 6 quark flavours separately (as i.e. an antiquark is counted with the minus sign). They are conserved by both the electromagnetic and strong interactions (but not the weak interaction). From them can be built the derived quantum numbers: Hypercharge (): Electric charge (): (see Gell-Mann–Nishijima formula) The terms "strange" and "strangeness" predate the discovery of the quark, but continued to be used after its discovery for the sake of continuity (i.e. the strangeness of each type of hadron remained the same); strangeness of anti-particles being referred to as +1, and particles as −1 as per the original definition. Strangeness was introduced to explain the rate of decay of newly discovered particles, such as the kaon, and was used in the Eightfold Way classification of hadrons and in subsequent quark models. These quantum numbers are preserved under strong and electromagnetic interactions, but not under weak interactions. For first-order weak decays, that is processes involving only one quark decay,