Brings back memories. I remember levelling across a bridge in Co. Cork when the staff began to look blurred through the level. Yep you guessed it, there was a train coming. Had to put the level and tripod over my shoulder and run like mad closely followed by the bloke with the staff. Looking back it was like something from a Bugs Bunny cartoon. At the time it was adrenaline pumping to say the least. Ah the late 70's, wonder how I ever survived into the 80's....