| 41. | When comparing RO and carbon block systems, Hammer notes that carbon blocks are less costly to maintain and repair.
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| 42. | With the ECO-Block system, Cotton said, a house starts out as a hollow-walled shell made of expanded polystyrene foam.
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| 43. | As with most modern roller coasters, a block system keeps trainsets moving and prevents trains from colliding with each other.
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| 44. | RO systems waste two gallons of water for every gallon filtered, while carbon block systems filter continuously with regularly changed filters.
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| 45. | In both systems, a distant signal tells the driver the aspect of the following home signal according to the Block system.
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| 46. | Another common block system exists in which students spend up to 100 minutes per class, and earn four credits each semester.
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| 47. | Manual block systems work by dividing up a rail line into predefined " blocks ", which are typically demarcated by fixed signs.
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| 48. | This formerly served as the control centre while the line was signalled using the Radio Electronic Token Block system ( RETB ).
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| 49. | The electric telegraph provided the ability for signalmen to communicate with each other and provided the basis for the absolute block system.
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| 50. | This manual block system is still on use on the Long Island Rail Road, which had been a subsidiary of the PRR.
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