Rule 711.5 · Leveler Cards
If the number of level counters on a leveler creature is less than N1 (the first number printed in its {LEVEL N1-N2} symbol), it has the power and toughness denoted by its uppermost power/toughness box.
Ask the judge Pro
The life counter has an AI judge that answers your play citing the exact rules. It is part of Gatewatch Pro; the rules, Oracle text and rulings stay free.