【Adjust】 , 【regulate】 and 【fix】 share the meaning to set right or to rights.

【Adjust】 implies modification to meet a need. To 【adjust】 a thing one brings it by some change into its exact or proper position or condition or into its right relationship with other things.

One adjusts a telescope when one changes the distance between its eyepiece and its object glass so as to bring it into focus; one adjusts the temperature of a house when one changes the setting of a thermostat. Often 【adjust】 implies rectification or correction.

• 【adjust】 an error in an account
• 【adjust】 a loose screw in a machine
• 【adjust】 spectacles that are not properly centered

Frequently it suggests straightening out or settling.

• 【adjust】 a difficulty with a neighbor
• 【adjust】 a claim for insurance

【Regulate】 , on the other hand, usually implies the maintenance of something in a desired condition.

To 【regulate】 something (as a mechanism, a device, an organ) one uses or serves as the means of making it work or operate regularly, uniformly, or accurately; thus, one regulates a clock when one adjusts its mechanism so that it will keep accurate time.

• some drugs 【regulate】 the beat of the heart by slowing it up, others by hastening it, until its rate of speed is normal

One also regulates something that is produced or effected by a mechanism or a bodily organ when one uses the means to keep it at a fixed or uniform rate or degree.

• 【regulate】 the temperature of the house by setting the thermostat at the desired mark and keeping it there

【Fix】 is an informal and imprecise equivalent to these words. It is often used where 【adjust】 or 【regulate】 would be more explicit and effective.

• the optician will 【fix】 her glasses
• please 【fix】 the clock
• he will 【fix】 up matters for us

In distinctive use it implies restoration to good order or a state of repair.

• these shoes are not worth fixing
• fixed the leak in the roof