The Hewlett-Packard Co.

Hewlett-Packard

Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...

markets the hp 33s calculator. Main features:

• RPN or traditional semi-algebraic (infix data/algebraic operator entry/postfix one-number function entry), user selectable
• Two-line LCD display
• Full scientific/engineering mathematical features
• Keystroke programmable with full boolean and program control command sets and line edit, insert and delete
• HP "equation list" equation editor (fully algebraic) in both the stand-alone list as well as in keystroke programs
• HP Solver feature (solves equations and functions for one unknown)
• Function integration feature
• All mathematical operations and features fully functional in all modes
• Unit conversion & constants
• 31 kilobyte
  Kilobyte
  The kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...
  
  s of random-access user memory (equivalent to about 7k on earlier HP programmable models)

HP 33s is designed by Kinpo Electronics, Inc.

It is generally considered to have fewer bugs than the HP 35s

HP 35s

The HP 35s Scientific Calculator is, as of 2007, the latest in Hewlett-Packard's long line of non-graphing scientific and programmable calculators...

, however with an inferior keypad layout - especially the size and placement of the "Enter" key.

According to numerous posts on the HPMuseum Forum (linked below), the 33s has been through numerous revisions that has solved two of the most pervasive issues people had with the early models (namely poor screen quality and bad keypad responsiveness).