Thanks gents.
I question why are the results not the same?
[H4]=ISBLANK(B3:B5) >> true
[H6]=ISBLANK(B3:B5) >> false
As far as I am convinced, the returned value should be TRUE in H4 as well as H6.
The plan was to sum points on a score card. The score values are integers <0;10>, additional possible characters are "-", "x" or an empty cell. To make the form look neat, I desire not to see "0" as the sum of the column until at least one of the scores is entered. My solution was this: =IF(ISBLANK(B3:B5);"";SUM(B3:B5)). Plain language: if the score column is completely empty, show no character, otherwise show the sum of score column. But I did not get what I intended so started troubleshooting. The above is where I got stuck.