Remember not to press too hard on the keyboard as this will caus a hard reset. Not sure if this happened with all ZX81 models, but on a friend's model we had to

Remember not to press too hard on the keyboard as this will caus a hard reset. Not sure if this happened with all ZX81 models, but on a friend's model we had to be very careful when entering our elaborate programs not to cause a reset by typing too hard.