APx500 measurement software for all APx Series instruments. Important: APx500 v4.5 requires a Windows 64-bit operating system. This download is suitable for most users. If Microsoft .NET version 4.5 is not already on your PC, it will be downloaded during the installation. For PCs that do not have .NET version 4.5 installed, and are not connected to the Internet, download the full installer instead (APx500 Measurement Software (with .NET)) NOTE: .NET 4.5 does not support Microsoft Windows XP.