In this case, the interval is between ambient pressure (0 atm) and 3.0 GPa.
The arrow in (a) shows the enhancement of Tc that occurs between <measure type="interval"><measure type="PRESSURE">ambient pressure</measure> and <num atMost="3.0">3.0</num> <measure type="PRESSURE" unit="GPa">GPa</measure></measure>.
The current notation seems to have some limits, unless we add the attribute atLeast/atMost also to the <measure> tag.
Any idea?