The nice thing about working in #"cal"#s is that the specific heat capacity of water is unambiguously #"1 cal/g"^@ "C"#. With #"J"#, some places define it as #4.184#, some other places define it as #4.186#, and yet other places define it as #4.181#... that you should specify your source if you want to be precise. With #"cal"#, you know it's #1#.
The specific heat capacity is the amount of heat (e.g. #"cal"#, #"J"#, etc) that needs to be added for every #"g"# of substance you have in order to raise the bulk substance's temperature by #1^@ "C"#.
So if #s_w = "1 cal/g"^@ "C"#, then you would need #"1 cal"# to raise the temperature of #"1 g"# of water by #1^@ "C"#.
