The smallest collecting area unit on the telescope surface at MOST is termed a “module”, and has an area of approximately 50 square metres. There are 352 modules, for a total collecting area of approx. 18,000 square metres. Four modules make a “bay”, of which there are 44 in each of two arms – one in the East and one in the West. Each module is a bay is assigned a colour (red, yellow, green and blue), as shown below. Groups of 16 modules (or 4 bays) are called a “Bay Group” — each of these feeds into a PFB (Polyphase filterbank) via a dedicated optical fibre bundle.