Wierd summation error.

Well I’m adding cell values along a diagonal and in one series I get 1+1+0 the cell where it adds together gives 1.66667 as the answer. I’ve reproduced this in other cells as well. Is there a setting I’m missing somewhere or what?

You fail to give some important information - LO version, O/S, what format are you using in the cells, what is the equation giving the result. Please edit your question to include these. I have tried to duplicate in LO v5.1.1.3 Linux on a clean sheet & answer is always 2.