Alternatively, if you know that you will only ever be filling values / data from a known and fixed list, consider using a 'List Box' - it will offer a list of the 'correct answers' and you just pick the one you want. It makes life a lot easier later, when you realise you have not spelled the...
"When making an entry in a cell, OpenOffice Calc automatically suggests matching input found in the same column. This function is known as AutoInput.
To turn the AutoInput on and off, set or remove the tick mark in front of Tools - Cell Content - AutoInput."
From the Help file in OpenOffice.
If...
"trying to make use of the predictive function" - I am not sure what you mean by that.
Can you post a screenshot of a sample of your sheet, or give a description of what it is you are trying to do? Which Function are you using - an in-built one, or an externally-supplied one? Or are you simply...