Olefin feeds with high olefin content andor containing a substance that generates water when contacting the catalyst, are oligomerised over solid phosphoric acid catalyst in tubular reactors by introducing the olefin feed into the reactor and maintaining the reacting mixture under conditions whereby the peak temperature is controlled to be below 265\xb0 C. for at least two hours, and then heating the ampoule at a temperature between 550 and 950 \xb0 C. A first glass substrate is provided which has at least one of cavities and openings at the bonding surface. A lamp output determination is performed at a predetermined time before shifting to the third phase, and upon determining that the lamp is ignited the second phase is inserted. The footpeg arm includes an attachment portion pivotally coupled to the footboard about a pivot axis that is not parallel to the foot support plane.