The bomb calorimeter method delivers very accurate results. The idea is execute the reaction adiabatically - meaning no heat loss from the system. The compound undergoing combustion is electrically ignited, and does so under pressure in an atmosphere of pure oxygen gas and this ensures complete and rapid combustion. There may be several water baths and thermometers to make sure every joule of energy released is monitored.
The heat capacity of a bomb calorimeter can be very accurately determined by combustion of a standard substance like benzoic acid whose enthalpy of combustion is known from previous experiments.
The bomb calorimeter method involves measuring the heat released at constant volume and is strictly speaking called the internal energy change ΔE or ΔU. Methods 1.3a1 and 1.3a2 involve heat energy changes at constant pressure ΔH. From 1.3a bomb calorimeter measurements you can calculate the enthalpy change from the equation
ΔH = ΔE + ΔnRT (n = the net change in moles of gas in the reaction) I don't think this equation is needed for any UK pre-university advanced level chemistry course these days?
If there are no gaseous reactants or products (i.e. only liquids/solids involved) OR if moles gaseous reactants = moles gaseous products, then Δn = 0 and ΔH = ΔE or ΔU).