trouble using sum command

[moneypenny]

I have a mileage spreadsheet with columns for start of journey and finish mileage, the next column is the difference between the first two figures, when I use the sum command on the difference column the answer is different to the start and finish difference, using one or two examples gives the correct answers, over many entries(200+) and the answers differ by 2000 miles, can you be of assistance?

Thankyou
moneypenny

[mikekaganski]

An example file with a problem please. See here for an example, when a similar problem was unsuccessfully discussed until a sample came, and then it only took a couple of minutes to solve.

[mariosv]

Pls inform also about your LlibreOffice version, If I remember right, about a year ago there were issues with OpenCL enable (Menu/Tools/Options/LibreOffice) with ranges large than 100 cells.