If you do not have the Go Direct^® Energy Sensor (GDX-NRG), Vernier Energy Sensor (VES-BTA), or the Differential Voltage Probe (DVP-BTA), and the Current Probe (DCP-BTA), you can purchase inexpensive multimeters at a number of online and brick-and-mortar shops.

Try:
Harbor Freight (online and brick-and-mortar) Item # 98025
Home Depot (online and brick-and-mortar) Model # MAS830B Store SKU # 119701
Maker Shed (online) Item #MKME02
All Electronics (online) Item #DVM-810 or #DVM-850BL
Mouser Electronics (online) Item #992-DMM-899
*Vernier Software & Technology cannot make guarantees about the pricing or availability of these items.

The KidWind MINI Wind Turbine with Blade Design (KW-MWTBD) includes a digital multimeter.

The following KidWind wind turbine kits do not include a digital multimeter:
KidWind Advanced Wind Experiment Kit (KW-AWX)
KidWind Advanced Wind Experiment Kit (KW-AWXC)
KidWind Basic Wind Experiment Kit (KW-BWX)
KidWind Basic Wind Experiment Kit (KW-BWXC)
KidWind MINI Wind Turbine with Blade Design (KW-MWT)