Manchester - The Decision Review System and the vexed question of when umpires should be helped by technology have been behind several talking points this Ashes, with Australia batsman Usman Khawaja's dismissal in the third Test at Old Trafford on Thursday the latest.
Below is a looks at some of the more controversial decisions.
First Test, Trent Bridge:
Ashton Agar (AUS): The 19-year-old debutant appeared, to many judges, to have been stumped on six but third umpire Marais Erasmus ruled in the batsman's favour and the teenager went on to make 98 -- the highest score by a Test match No 11.
Jonathan Trott (ENG): Erasmus was again centre stage when the South African overturned experienced Pakistani on-field umpire Aleem Dar's original not out decision and instructed him to give the England batsman out lbw. As the host broadcaster was using Hotspot to illustrate a replay of the previous wicket, the thermal imaging system was not available to Erasmus.
Stuart Broad (ENG): Australia and numerous observers were left stunned when Broad stood his ground after his thick edge went off wicketkeeper Brad Haddin's gloves to Australia captain Michael Clarke at slip only for Dar to rule not out. As Australia had used up all their reviews, Broad remained and his conduct reopened the debates about 'walking' and whether officials should have control of the DRS without teams needing to call for a review.
Second Test, Lord's:
Chris Rogers (AUS): Rogers somehow missed his attempted pull at an accidental full toss from Graeme Swann, a ball the off-spinner later said was the worst he'd bowled, and was struck at box height. Erasmus upheld England's lbw appeal and Rogers opted against a referral. But replays showed the ball missing leg-stump.
Ian Bell (ENG): Having made back-to-back centuries, it seemed Bell was out for three when Steven Smith claimed a low catch at gully. The on-field umpires passed the decision onto third umpire Tony Hill and, as is often the case in such circumstances, he ruled in the batsman's favour even though many former players were convinced replays showed the catch had been taken cleanly.
Third Test, Old Trafford:
Usman Khawaja (AUS): After being given out for a single by on-field umpire Hill, caught behind off Swann, he immediately reviewed the New Zealander's decision. DRS appeared to indicate there was no noise at the moment the bat ought to have hit the ball and nor did Hotspot reveal an edge.
Yet Sri Lanka's Kumar Dharmasena upheld Hill's decision, prompting Australia great Shane Warne to label the decision "absolutely shocking", with Australia Prime Minister Kevin Rudd calling it one of the worst he'd seen.
Steven Smith (AUS): Having survived two England reviews, the all-rounder was plumb lbw on 24 to Stuart Broad only for Hill to somehow rule not out.
Now it was England's turn to be frustrated by having already used both their reviews for the innings.