First, check that you indeed used the Polar Cloud build plate “SCALE” feature to request exactly the desired object size: the requested object size is displayed via the build plate screen’s size boxes, when the “UI SETTINGS” switch “Show object dimension in mm” is enabled. (To check requested print object size for a currently queued print job, go to the printer queue or your account “QUEUED” screen, select the print job from the queue, click the three vertical dots to open the job modification menu, and select “Edit Job” to return to the build plate screen; for a finished print job, go to the printer or your account “HISTORY” and select the print job, click the three dots to open the job retrospect menu, select “Requeue Job” to re-submit the job again, and then follow the steps for inspecting requested object size for a queued job.)
Now keep in mind that different filament types may exhibit different amounts of shrinkage during cooling while and after printing. For instance, if you are printing an object using ABS filament you will may need to “size up” the object a bit compared to printing that same object using PLA filament.
Next, note that the initial layer of your object (which for adhesion purposes is often printed a little extra close to, and hence “smooshed”, on the build platform) may vary from the general dimensions of your object – and indeed the first few layers, connecting to the initial layer, may also suffer a bit of distortion in size. So when you’re measuring the dimensions of your printed object, make sure to measure it after a number of layers – be clear on whether there is an overall size issue, vs. whether merely the first few layers are a little too big.
If the issue is merely the first few layers, then you will want to take steps to have the first few layers conform to the overall desired size, while still achieving good adhesion. You may want to print with a raft to achieve good adhesion (while leaving the printer’s z height calibration for “smooshing” the first layer unchanged, with that “smooshing” now allowing the raft to adhere rather than impacting the object’s own first layer), and then set initial layer adjustments for the object itself such as “First Layer Extrusion Width” and “Initial Layer Thickness” (under “PRINT SETTINGS”, “ADVANCED”) to match the regular settings for later layers (“Extrusion Width” and “Layer Thickness”).
If you are seeing a constant-throughout-the-object error in dimension size, then measure your filament diameter very carefully, using calipers, and under “PRINT SETTINGS”, “BASIC”, adjust the “Filament Diameter” setting accordingly; an actual filament diameter different than your printer expects will result in over-extrusion or under-extrusion and a corresponding skew in object size. If you have already checked the filament diameter and are still seeing a bit of over- or under-extrusion, then note that the “Filament Flow” setting (under “PRINT SETTINGS”, “ADVANCED”) can be used to fine-tune the printer’s extrusion of filament.
If you have tight tolerances for subtle size variations over an object surface, also check that your number of shells (see the settings under “PRINT SETTINGS”, “ADVANCED”, “Quality”, especially “Wall Thickness” and “Top Layer Count”) are suitable for the “Infill Amount” and “Infill Overlap” you are using: too few shells (too thin of an object exterior) combined with low “Infill Amount” can result in sagging of the object exterior into the interior (see item 14), or too few shells combined with higher “Infill Overlap” can result in a bit of bulging where the infill lines or grid overlap with (bond with) the innermost shell of the exterior.