'too close to call'
As votes are counted for each electoral area, the numbers go up on the board.
Now, there are a definite number of registered voters per constituency. If there are 100 people voting (say), and one candidate has polled 40 and the other 44, that means there are 15 votes still to be counted.
If one or other of the candidates received ALL those votes, then the possible final votes would be either 55, or 59. But because the voting is already so close, they are likely to continue neck and neck. What say later votes swing in favour of the candidate with 40 votes so that he takes the lead?
It's just 'too close to call' - the numbers of votes for both candidates are so close, it is not possible to predict the end result (call) - who will win this seat - at this point in time.
Student or Learner