Vintage 1948 Time-Tab Sliding Elapsed Time Calculator For Sale

For sale is this very rare historically significant Time-Tab Elapsed Time Calculator. This mechanical slide calculator was designed to quickly compute elapsed time between two points, like start and end times for flights, train schedules or work shifts. This unit was invented by R.E. Freeland in 1948. This was used before digital calculators and computers. The unit pictured is very well built. The face is made of stainless steel. The sliding bars are made of aluminum. The rest of the body is made of wood. The stylist pen-like object is made of aluminum. The 2 bars slide on what appears to be felt. The overall condition is very good. There are light scratches but not really much that stand out. The 2 bars slide very nice with use of the stylist. The total length of the calculator is 20 in. long. Each bar is 19 3/4 in. long by 3/4 in. The sliding pen is 4 3/4 in. long. The stainless steel face is 3 in. The other 2 wood sides are each 2 1/4 in. Besides the Time-Tab decal the other writing is located on the upper bar and it reads \"Copyright 1948 R.E. Freeland.\" The unit weighs 2 lbs., 4 oz. There is a designated slot for the pen/slider on the right side. Somebody had put some tape over the slot most likely for travelling.