Possible Clues:

• It's taut up to nine, by the sound of it, perhaps
• That'll teach you not to reach double figures, by the sound of it
• May be no nore than nine, by the sound of it
• Perhaps under 10, by the sound of it, one learns
• It takes under X, perhaps, to get taut, by the sound of it
• By the sound of it, not so much as X to be learned from this
• Learn from this that there's not so much upon X
• 'This teaches one only till nine, by the sound of it (6,3)'
• Not so much on X to be learned from this