Macro for calculation and user entry in same cell?

A friend told me that I could probably do this with a macro ... but I have no idea how. Can anybody help me accomplish this?

Here's the problem:
Say I start off with an amount in cell: D104
(For grins, say the amount is: (5)

Now ... say I later enter amounts in cells: H95 through H102
(say, the amount entered in each of these cells is: (1)

Is there a way via a macro or VB to add the amounts in (H95:H102) to the already existing amount in (D104)?

In the example I explained above ... the total would be: (5+1+1+1+1+1+1+1+1)=13

Thank you!

it could be done by a macro but you risk corupting you data for example you have h in h95 you add ather number in other cells and you end up with 13 in h95 you then change h97 from 1 to 4 h95 would become 17 as the macro has no way of knowing what your original starting number was in h95.

It would be better to use a sum formula than a macro