I'd be inclined to stick with the three separate fields for doing finds. The use simply has to press a key (tab is the default) to move from field to field so I don't see that there is much convenience to using the calculation field for entering find criteria and there are some finds that will produce different results when using the calculation field compared to what you would get using the separate fields.
You might be right, Phil. It's just that, when you look at the layout in find mode, there isn't any particularly obvious division between the fields so you just have to know to click about the middle or towards the right-hand side.
Thanks, though, for taking the time.
I'd add field borders and field labels so that this is obvious and as I mentioned earlier, you don't have to click to select the other fields, you can press tab to move to the next field in the tab order.