article_snippet: Above, a pupil uses plastic balls to train .
article_snippet: A butter-knife laid a centimetre out of place can lead to failure.
article_snippet: Using rulers to make sure the distances are correct is not unknown.
article_snippet: Another student Chrissy Yan described the training - especially laying a table - as 'hard'.
article_snippet: students fail if students are a centimetre out of place .