10" Engineering Instruments Slide Rule Model 250-BT W/ Case

Vintage 10 Inch Slide Rule Engineering Instruments - Model 250 BT Peru Indiana

Vintage Engineering Instruments 10” Slide Ruler Model 250 -V

Engineering Instruments Model 250-V 10 Inch Slide Rule w/Instructions & Case

Slide Rule - Engineering Instruments, Inc. 250-V w/case & instructions

Vintage 10 Inch Slide Rule Engineering Instruments - Model 250 BT Peru Indiana

Lawrence Engineering Instruments 250-V Slide Rule Peru Indiana Vintage

Vtg (1950s?) Engineering Instruments Model 10 B 10” Slide Rule w/Booklet