N = PC / #Shares and then for next trade prices dividing N by 0.85 and N by 1.15 (for 10% safe, 5% minimum trade size) just needs a basic calculator.
You could use a tablet or phone I guess, but past experiences have expressed how relying upon 'data' (electronic storage) can be flawed. Less so now with the cloud, but in the past I've had hardware fail only to then encounter restore from backups failure.
Plus I hate wearing glasses and I can't see the tiny text on phones without such aid.
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