PIRA Classification: 2A10.10
Description: A light metal frame is rigid on three sides. The fourth side consists of a sliding fine wire. The wire is slid toward the opposite side and the frame is dipped in a soap solution. The frame is then placed on the overhead projector. The tension of the wire is adjusted until it moves freely.
Special Instructions: None
Condition: OK
Setup time: 1 minute
Safety Issues: None