     rx3.close()
     XCTAssert(rx3.isClosed)
 
-    let dt = mach_absolute_time() - start
+    let dt = mach_absolute_time()*UInt64(scale.numer)/UInt64(scale.denom) - start
     XCTAssert(dt > numericCast(2*delay))
   }
 

class TimeoutTests: XCTestCase
{
  let delay: Int64 = 50_000

  func testTimeout()
  {
    let start = mach_absolute_time()

    let time1 = dispatch_time(DISPATCH_TIME_NOW, delay)
    let rx1 = Timeout(time1)


    for var i = 0, j = 0; i < 10; j++
    {
      let start = mach_absolute_time()*UInt64(scale.numer)/UInt64(scale.denom)
      let timer = Timeout(delay: delay)
      if let selection = select_chan(selectables + [timer])
      {
