"1-a. For small aeroplanes, they can't actually climb when the gear is down, so you have to retract it right after full power is applied, otherwise it will never climb in some conditions."
So how did the plane get off the runway so you could retract the gear? Or are we talking twins? There are some twins that won't climb even with the gear up on one engine. Just prolongs the agony.
Personally I use the altimeter.