As others prior to my entrance have occasioned, this particular piece is rather rough on the obverse(face) of the coin, the flan cracks and porosity are a bit of a turn off. Most of the Ryals from the 1566-1572 era were called in and counterstamped with the thistle to raise the value of the coin from 30/- to 36/9 in 1578, effectively realising that again inflation had once again eroded Scottish sterling. I suspect that your grandfather paid rather too much dosh for said piece if indeed it was purchased 50+ years ago, it's value now is subjective as others have pointed out. The catalogues for Scottish coinage are becoming rather dated and have never been in touch with reality pricewise. Choice, problem free material on the auction circuit advances considerably in price, and I myself have paid significantly more than a catalogue price for choice materiel, but most Scottish materiel circulated a long time and is not choice by any stretch. This piece appears to be in no better than a fine grade by my estimation, indeed it is worth a bit more than what was paid years ago, but only about 300-350 Quid or so.