Apple’s stock set an all-time high yesterday as investors awaited the launch of the iPad tablet computer this weekend. Apple shares hit US$233.87 in Monday morning trading on the Nasdaq stock market. The stock has risen about 15 percent since the company introduced the iPad at a media event in late January, and has more than doubled from its level at this time last year. Forecasts for first-year sales vary widely — from 2 million to 5 million units — reflecting the difficulty in predicting the size of a yet-to-be-proven market.