The monthly sales reached $100,000 in March 1973, and MITS moved to a larger building with 10,000 square feet (930 square meters) of space. In 1973, MITS was selling every calculator that they could make, and 110 employees worked in two shifts assembling them. The functionality of calculator integrated circuits increased at a rapid pace and Roberts was designing and producing new models. The popularity of electronic calculators drew the traditional office equipment companies and the semiconductor companies into the market. In September 1972, Texas Instruments (TI) introduced the TI-2500 portable four-function calculator that sold for $120. The larger companies could sell below cost to win market share. By early 1974, Ed Roberts found that he could purchase a calculator in a retail store for less than his cost of materials. MITS was now $300,000 in debt, and Roberts was looking for a new hit product.