One of the iPhone/iPad apps I have depended on for a long time is called "Machinist Journeyman". Best $9.99 I've ever spent. I recommended it to someone here a while back and after they and I checked the app store it was no longer listed. I was really concerned since I had received several warnings that this app might not work after the next system upgrade. Finally gave in and let my phone upgrade the IOS and lo and behold not only did that app work but it had been upgraded to a new version. I checked the app store and it is listed again as being available for purchase. For what I need to do it works very well and I recommend it highly. I've tried numerous other iPhone machinist's apps and so far this is the best I've found. Note that I am in no way associated with the developers or Apple or any other party that might profit from this, I'm just a happy user.