K&E 4135 Family of Slide Rules
The 4135 and N4135 Power computing slide rules were specially designed for power calculations that relate to
The 4135 was offered between 1913 and 1921. It is a 7 inch duplex rule with two slides and no cursor.
4135 --- 7 " Power Computing Slide rule. No serial number. Early form with multiple slides.
The N4135 replaced the 4135 in 1922 with a significantly different format. It is a 5 inch duplex rule similar to the 4088-1.
N4135 - 5" Power Computing Slide rule. Serial number 361316.