Hi Plot Plot,
To begin with you have to calculate the pressure altitude to then find out your temperature deviation from ISA. So In the example you’ve used, the QNH is 1001, cruising Altitude is 7000ft and the OAT is -14.
Firstly you’ve got to work out the pressure altitude, so for this example - (1013-1001) x 30 = 360ft. We then add this to our cruising height of 7000ft, so 7360ft.
We then round the 7360 to the nearest 500ft which is 7500ft giving a ISA temp of 0 degrees, thus a deviation of 14 degrees. Hopefully this changes your answer, if it doesn’t I’ll dive a little deeper when I get him from work. Also remember that your CR3 isn’t the most accurate piece of machinery.
Cheers,