Excel does not sum correctly

[Steve Urich]

this is the sum StatementThe numbers just don't add up

The top pic is the formula. 

The bottom pic is p18 to x18 and the numbers don't add up

Suggestions on how to fix and what is causing the problem.

Scary if you can't trust Excel to add correctly.

[#2]

Is there a number in the hidden column F? or do you have any other hidden column?

[#3]

@Steve Urich 

The chance that Excel has performed the summation incorrectly is so small that it is hardly worth considering.  The chance that it has performed an incorrect summation is far greater since it is the user that specifies the calculation and error is a fundamental part of human behaviour.

The first thing I would observe is that Excel has flagged every 'incorrect' result with a green marker in the cell corner.  I cannot tell what is wrong from a picture but the error flag should provide a clue.

[#4]

En Español:
Buen día,
Haga la siguiente prueba:
1.- Seleccione toda la hoja,
2.- En la pestaña Inicio, Edición, Borrar => seleccione el botón de borrar (droop down)
y seleccione borrar formatos.
3.- Compruebe que todos las celdas con números están alineadas a la derecha,
Si no es así, es que alguna celda no está en formato de número, o que el formato oculta
decimales que crean resultados aparentemente falsos.
El hombre comete errores, las máquinas hacen exactamente lo que se les pide.

[#5]

@Peter Bartholomew 

 Hidden column. There was a column that was hidden but still calculated.

[#6]

@srdobrais 

Thanks for your help