To help us obtain an accurate value for the specific heat capacity of water, we put insulation round and on top of a beaker of water. We weighed the water and measured the temperature rise for the water over a 15 minute period. We calculated the energy we put in by using E = ItV so that's current from the ammeter x time in seconds x voltage. Then specific heat capacity = E/(mass x temp rise). No insulation would have meant a smaller temperature rise for the same energy and hence a value for SHC that would have been too big. Accurate means getting the right answer.
