The most common and most likely answer to this crossword clue is the 6 letter word METERS
M
E
T
E
R
S
Buddy explains!
The straight part
We know that "They calculate" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they calculate = meters.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does METERS mean?
METERS noun- (always meter) A device that measures things.
- (always meter) A parking meter or similar device for collecting payment.
- (always meter) One who metes or measures.
- (elsewhere metre) The base unit of length in the International System of Units (SI), conceived of as 1/10000000 of the distance from the North Pole to the Equator, and now defined as the distance light will travel in a vacuum in 1/299792458 second.
- (elsewhere metre) An increment of music; the overall rhythm; particularly, the number of beats in a measure.
- (elsewhere metre) The rhythm pattern in a poem.
- (elsewhere metre) A line above or below a hanging net, to which the net is attached in order to strengthen it.
- A poem.
- To measure with a metering device.
- To imprint a postage mark with a postage meter.
- To regulate the flow of or to deliver in regulated amounts (usually of fluids but sometimes of other things such as anticipation or breath).