Editing Altair 8800 (section)

===Calculators===
The model rocket kits were a modest success and MITS wanted to try a kit that would appeal to more hobbyists. The November 1970 issue of ''Popular Electronics'' featured the Opticom, a kit from MITS that would send voice over an [[LED]] light beam. As Mims and Cagle were losing interest in the kit business, Roberts bought his partners out and began developing a calculator kit. [[Electronic Arrays]] had just announced the EAS100, a set of six [[Integrated circuit#SSI.2C MSI and LSI|large scale integrated]] (LSI) circuit chips that would make a four-function calculator.<ref name = "Calculator Patent">{{US patent reference | number = 3800129 | y = 1974 | m = 03 | d = 26 | inventor = Richard H. Umstattd | title = MOS Desk Calculator}}</ref> The [[Micro Instrumentation and Telemetry Systems#Calculators|MITS 816]] calculator kit used the chipset and was featured on the November 1971 cover of ''Popular Electronics''. This calculator kit sold for {{US$|long=no|175}}, or $275 assembled.<ref name = "MITS 816">{{cite magazine | author = Ed Roberts |date=November 1971 | title = Electronic desk calculator you can build |magazine= Popular Electronics | volume = 35 | issue = 5 | pages =27–32 | publisher = Ziff Davis}}</ref> Forrest Mims wrote the assembly manual for this kit and many others over the next several years. As payment for each manual he often accepted a copy of the kit.

The calculator was successful and was followed by several improved models. The MITS 1440 calculator was featured in the July 1973 issues of ''Radio-Electronics''. It had a 14-digit display, memory, and [[square root]] function. The kit sold for {{US$|long=no|200}} and the assembled version was {{US$|long=no|250}}.<ref name="MITS 1440">{{cite journal|last=Kellahin|first=James R.|date=July 1973|title=The 1440: A calculator with memory, square root and other new features|journal=Radio-Electronics|publisher=Gernsback Publication|volume=44|issue=7|pages=55–57}} The cover story is for the MITS 1700 waveform generator. An ad for the MITS 1200, a {{US$|long=no|99}} battery operated handheld calculator, is on page 15.</ref> MITS later developed a programmer unit that would connect to the 816 or 1440 calculator and allow programs of up to 256 steps.<ref name = "Calculator Book">{{cite book | last =Roberts | first =H. Edward | author-link = Ed Roberts (computer engineer) | editor =Forrest M. Mims | title =Electronic Calculators | publisher =Howard W. Sams | year =1974 | pages = 128–143 | isbn = 0-672-21039-8}}</ref>

In 1972, [[Texas Instruments]] developed its own calculator chip and started selling complete calculators at less than half the price of other commercial models. MITS and many other companies were devastated by this, and Roberts struggled to reduce his quarter-million-dollar debt.