The unique Jenerates Crochet Ruler - in centimetres or inches.  Unique because the ruler starts at zero at both the inside and outside corners, which means you can use it whichever way best lets you see your work.  The crochet hook gauge is shaped so the hook fits through to let you measure the shaft.  The metric ruler covers 2mm to 8mm (14 - 0 uK / A - L US on the imperial version) and the ruler fits a standard size tension square exactly.    
 
Let me know if you would like a gift message printed with your purchase - there's a box for that in the checkout.  
 
If you're buying from outside the UK - please buy through Etsy to have the correct tax applied. This should save you paying your local handling charge in addition to any tax.