Next, you need to define increment and decrement methods. Both do their
work on the value holder found via the meterValueHolder
getter:
MeterDemonstration method definition instance incrementMeter | valueHolder | valueHolder := self meterValueHolder. valueHolder value: valueHolder value + 1. MeterDemonstration method definition instance decrementMeter | valueHolder | valueHolder := self meterValueHolder. valueHolder value: valueHolder value - 1.