Not sure i can see why you would need to lock it just move the dot up until you get the number of credits you want then laterally to splitt between research and production...or am I missing something?
It's not really laterally, you have to move in curves like Darca noted. It isn't difficult without the ability to lock, but adding the lock would be a bit of a time saver, especially if you want to experiment a little with what different levels of the other two would give you.
