Page 485 - Practical English Usage 3ed - Michael Swan, Oxford

present tenses (5): stories, commentaries and instructions 465
8 how long1 present tenses not used
We use a perfect tense, not a present tense, to say how long something has been going on. (See 460 for details.)
I've been learning English for three years. (NOT I'm leaffling English for three yetm.)
465 present tenses (5):
stories, commentaries and instructions
1 stories
Present tenses are often used informally to tell stories. The simple present is used for the events - the things that happen one after another. The present progressive is used for 'background' - things that are already happening when the story starts, or that continue through the story. (This is like the difference between the simple past and past progressive: see 422.)
So I open the door, and I look out into the garden, and I see this man. He's wearing pyjamas and a policeman's helmet. 'Hello,' he says ...
There's this Scotsman, you see, and he's walking through the jungle when he meets a gorilla. And the gorilla's eating a snake sandwich. So the Scotsman goes up to the gorilla ...
The simple present is common in summaries of plays, stories, etc.
In Act I, Hamlet sees the ghost of his father. The ghost tells him . .. Chapter 2: Henry goes to Scotland and meets the Loch Ness Monster.
2 commentaries
In commentaries, the use of tenses is similar. The simple present is used for the quicker actions and events (which are finished before the sentences that describe them); the present progressive is used for longer actions and situations. There are more simple and fewer progressive tenses in a football commentary, for instance, than in a commentary on a boat race.
Smith passes to Devaney, Devaney to Barnes - and Harris intercepts . .. Harris passes back to Simms, nice ball - and Simms shoots!
Oxford are puUing slightly ahead ofCambridge now; they're rowing with a beautiful rhythm; Cambridge are looking a little disorganised . ..
3 instructions and demonstrations
We often use present tenses in a similar way to give instructions, demonstrations and directions.
OK. let's go over it again. You wait outside the bank until the manager arrives. Then you radio Louie, who's waiting round the corner, and he drives round to the front entrance. You and Louie grab the manager . ..
First I puta lump ofbutter into a frying pan and light the gas; then while the butter's melting I break three eggs into a bowl, like this . ..
How do I get to the station?...., You go straight on to the traffic lights, then you tum left ...
page 453