Methinks that the now-cheap handheld IR-Temp devices is the solution here; seen some ~$10=bargain.
I note that my freezer compartment, at 'Normal' setting gets 3-5º below 0 F reliably and I've calibrated the Chinese yellow device
(now small-thus-'hand'ier than the earlier models): via melting-ice+its H2O water == near-enough Lab-std accuracy;
mine happens to be within +/- a degree at that 32º F.
Concur ya need not -20, but allowing for temp-rise during inevitable Defrost periods: believe it safest to keep the sucker below -4F,
and if you ever keep $expensive viands for long periods.. going lower yet may prove cheap insurance, but YMMV.
(now small-thus-'hand'ier than the earlier models): via melting-ice+its H2O water == near-enough Lab-std accuracy;
mine happens to be within +/- a degree at that 32º F.
Concur ya need not -20, but allowing for temp-rise during inevitable Defrost periods: believe it safest to keep the sucker below -4F,
and if you ever keep $expensive viands for long periods.. going lower yet may prove cheap insurance, but YMMV.