In The Al Bida  1 Lloyd’s Rep. 142, per Evans J :
[T]he effect of the word "about" is that some margin must be recognised on either side of the stated figure. The size of that margin is a question of fact in the particular case, including where relevant, the influence of any trade or other recognised commercial practice, whilst the court retains the power to rule as a matter of law the margin cannot "reasonably" exceed or … be less than a certain figure.
In The Al Bida  1 Lloyd’s Rep. 124, per Parker LJ :
The margin imported in the word "about" cannot be fixed as a matter of law. The margin must, as the arbitrators rightly held, "be tailored to the ship’s configuration, size, draught and trim etc". There is no ground upon which the arbitrators can be required to state what the margin they have adopted.