Narrow-Angle Glass Prism, 30° x 75° x 75° Biology_Entomology & Zoology Economical minute timer setting intervals

Economical minute timer setting intervals up to one hour via a top knob

Molded black plastic replacement knob sized for the goggle sanitizer cabinet timer switch

exposing every wire and hammer so students trace the bell's electromagnetic action

Rounds out a comparative thermal-conductivity set with zinc at a moderate conductivity value

LED-output photoelectric cell on a 3

Narrow-Angle Glass Prism, 30° x 75° x 75° Biology_Entomology & Zoology Economical minute timer setting intervalsWider apex 30 x 75 x 75 glass wedge prism, the geometry approaching minimum deviation behavior where small apex shifts produce visible refraction angle changes.