The Portable CS did not succeed due to its large size (much larger than the Portable Plus), relatively high price and non-standard media (3.5 inch discs). The Portable was offered in two mass storage configurations: dual 3.5 inch (1.44 MB) floppy disc drives - P/N D1001A, or a floppy disc drive and a 20 MB hard disc drive - P/N D1009A. The Portable CS had a large LCD screen as well as CGA adaptor for use with an external monitor. The Vectra Portable CS was the portable version of the Vectra CS. Here’s the description from the HP Computer Museum : The company had high hopes for the portable, but it failed in the market. Hewlett-Packard introduced its Vectra Portable CS computer in 1987, and it contained a floppy disk drive and a 20 MB, 3.5″ hard drive. This is attributed mainly to the need to penetrate soils at greater depth than the top 2–3 mm, from which remote sensing data are collected. In contrast with remote sensing, proximal sensing has more emphasis on soil measurement than in crops. This is essential to explore the within-field spatial variability at sufficient resolutions to guarantee efficient site-specific management of soil and crop using variable rate technologies. Although the portable version is easy to use, it is labour-intensive in addition to the fact that the number of samples can be limited, compared with those collected by the online systems, which can reach up to 1000 readings per hectare or even more ( Mouazen and Kuang, 2016). Both for soil and crop, proximal sensors can also be classified as portable handheld, or online (here measurement is taken while driving across a field by means of a tractor or a quad bike). In comparison with remote sensing, with proximal sensing the sensor is placed in direct contact or within a distance of 2 m from the target ( Viscarra Rossel et al., 2011 ).
Sudduth, in Agricultural Internet of Things and Decision Support for Precision Smart Farming, 2020 2.3.1 A brief introduction to proximal sensing technology