Abstract: We have invented an improved apparatus for electronically measuring fluid flow. The apparatus includes a radiation detection means for indicating the position of a flow indicator in a chamber of a variable area flowmeter and has a reliability, versatility and functional accuracy not obtainable with known variable area flowmeters. The invention may also include a variable area flowmeter with the flow indicator in a tapered fluid flow chamber with a wall and a long axis, the chamber having a front side, a back side, and an operational length substantially parallel to the long axis. The invention has no moving parts and is not intrusive so mechanical malfunction and unwanted leaks can not occur. Useful embodiments include, for example, compact self contained apparatus useful for fitting around existing flowmeters, systems that include flowmeters and systems able to work with some fluids that are visually opaque.