I checked approx. 50 references for "waveform generation" "1 mHz" and found the following (all other shows “1MHz”:

In the past, waveform signals were generated with analog methods; older instruments used, for example, phase locked loops (PLL) to create a sine wave. Now, signals are digitized. This means that a signal generator approximates the signal curve with a staircase form (see Figure 1). The width (time scale) and height (amplitude scale) of each single step depend on the sample rate and the magnitude resolution. The smaller these steps are the better a signal can be reproduced.
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A “bandpass filter“ is used to filter out unwanted portions resulting in a smooth output signal. It removes the steps of the DDS output and prevents drifts in the signal. Following paragraphs illustrate this in more detail.
Figure 5 shows a 1 MHz sine wave output signal measured with an Interface 5000. The blue curve shows the output after the phase accumulator. Note that the clock frequency is 24 MHz. Hence a single sine wave exhibits 24 signal steps. The total signal is superimposed by high‑frequency noise. In contrast, the filtered output signal (red curve) is smooth and the staircase form is nearly completely filtered out. Further, the signal’s noise is also drastically reduced. The final output signal resembles more an analog signal.
[Figure 5]
Figure 6 compares the Fast‑Fourier‑Transformation (FFT) diagrams of both sine wave signals that are shown in Figure 5. The sine wave signals are displayed in the frequency‑domain. Figure 6A shows the unfiltered signal and Figure 6B shows the filtered signal.
Both plots show a major signal peak at 1 MHz which resembles the sine wave’s base frequency. Additional peaks can be found at the harmonics of the sine wave’s base frequency which is, in this case, n times 1 MHz (n = 2, 3, 4, …). These peaks are nearly completely filtered out by the filter as shown in Figure 6B.
[Figures 6 a&B]
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In contrast to high frequencies, low frequency signals can be controlled more easily because they resemble slow processes. Low frequencies do not have an instrumental but more a practical limitation. For example, a single sine wave of a 10 mHz signal lasts over 27 hours.
http://www.gamry.com/application-notes/EIS/waveform-generati...
Note: The remainders of harmonics distort the desired sinus wave and make it less accurate.

Function and arbitrary waveform generators are among the most important and versatile pieces of electronic test equipment. In electronic design and troubleshooting, the circuit under scrutiny often requires a controllable signal to simulate its normal operation. The testing of physical systems and transducers often needs stable and reliable signals. The signal levels needed range from microvolts to tens of volts or more.
Modern DDS (direct digital synthesis) function generators are able to provide a wide variety of signals. Today's basic units are capable of sine, square, and triangle outputs from less than 1 Hz to at least 1 MHz, with variable amplitude and adjustable DC offset. Many generators include extra features, such as higher frequency capability, variable symmetry, frequency sweep, AM and FM operation, and gated burst mode. More advanced models offer a variety of additional waveforms and Arbitrary Waveform Generators can supply user-defined periodic waveforms.
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This generator can generate 1 Hz to 25 MHz sine and square waves, 1 Hz to 5 MHz triangle and ramp waveforms, and 1 mHz to 10 MHz pulses. AM, FM, and FSK modulation are available (AM modulation can also be done on the arbitrary waveforms). The instrument comes with a serial port and an optional IEEE-488 GPIB port.
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Applications
Response testing with function generators
Stimulus-response testing is widely used to characterize behavior. Because many physical phenomena can be converted to and from electrical signals, a function generator is a good general-purpose stimulus source.
Frequency response measurement
A function generator can be used to characterize the frequency response of a system. This can be done manually, but it is labor-intensive and prone to errors. The operator sets the frequency, then measures the system's response. The results can be plotted with frequency on the horizontal axis and the response on the vertical axis. If the phase response can also be measured, a Bode plot of the system's response can be made.
Modern function generators often have the ability to sweep the frequency of the output signal. This is a fast way to characterize frequency-dependent behavior because it's easy to set up and display on an oscilloscope. We will briefly discuss how this can be done with older analog equipment, and then look at how it's done with modern DDS generators and digital oscilloscopes.
http://www.bkprecision.com/support/downloads/function-and-ar...

Arbitrary Waveforms
Arbitrary waveforms can meet needs not met by the instrument’s standard waveforms. For example, you might need a unique stimulus, or you might want to simulate signal imperfections such as overshoot, ringing, glitching, or noise. Arbitrary waveforms can be very complex, making them suitable for simulating signals in modern communications systems.
You can create arbitrary waveforms from a minimum of 8 points (33500 Series) or 32 points (33600 Series) up to 1,000,000 points. The instrument stores these numeric data points, known as "samples," in memory and then converts them into voltages as the waveform is generated. The frequency at which points are read is the "sample rate," and the waveform frequency equals the sample rate divided by the number of points in the waveform. For example, suppose a waveform has 40 points and the sample rate is 10 MHz. The frequency would be (10 MHz)/40 = 250 kHz and its period would be 4 µs.
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Quasi-Gaussian Noise
The Noise waveform is optimized for both quantitative and qualitative statistical properties. It does not repeat for more than 50 years of continuous operation. Unlike a true gaussian distribution, there is zero probability of getting a voltage beyond the instrument’s Vpp setting. The crest factor (peak voltage divided by RMS voltage) is approximately 4.6.
You can vary the Noise bandwidth from 1 mHz to the instrument's maximum bandwidth. The energy in the noise signal is concentrated in a band from DC to the selected bandwidth, so the signal has greater spectral density in the band of interest when the bandwidth setting is lower. In audio work, for example, you might set the bandwidth to 30 kHz, to make the audio band signal strength 30 dB higher than if the bandwidth were set to 30 MHz.
http://rfmw.em.keysight.com/spdhelpfiles/33500/webhelp/US/Co...

1mHz-10MHz Function/Arbitrary Waveform Generator with 50 MHz Frequency Counter & Time Mark
Scientech 4211 Function / Arbitrary Waveform Generator is based on Direct Digital Synthesis (DDS) technique to create stable, accurate output waveforms.
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Product Features
• Based on Direct Digital Synthesis (DDS) technique
• 3.5inch TFT True Color LCD
• Low distortion sine wave
• Square wave with fast rise & fall time
• 10 MHz Sine & 4 MHz Square waveform
• Pulse, Ramp, Triangle, Noise, and DC waveforms
• More than 25 Arbitrary waveforms
• 10bits, 100MSa/s, 4K points arbitrary waves
• AM, FM and FSK modulation types
• Sweep and Burst/ASK operation
http://www.scientechworld.com/test-and-measurement-solutions...

The Keysight Technologies, Inc. 33210A function/arbitrary waveform generator is the latest addition to the 332XX family. Waveforms are generated using direct digital synthesis (DDS) technology which creates stable, accurate low distortion sine waves as well as square waves with fast rise and fall times up to 10 MHz and linear ramp waves up to 100 kHz
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Waveform characteristics
Sine
Frequency range 1 mHz to 10 MHz
Amplitude
Flatness 1, 2
(relative to 1 kHz)
< 100 kHz 0 .1 dB
100 kHz to 5 MHz 0.2 dB
5 MHz to 10 MHz 0.3 dB
Harmonic distortion 2, 3< 1 Vpp ≥ 1 Vpp
DC to 20 kHz –70 dBc –70 dBc
20 kHz to 100 kHz –65 dBc –60 dBc
100 kHz to 1 MHz –50 dBc –45 dBc
1 MHz to 10 MHz –40 dBc –30 dBc
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Ramp, triangle
Frequency range 1 mHz to 100 kHz
Linearity < 0.1% of peak output
Variable symmetry 0.0% to 100.0%
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Footnotes
[1] Add 1/10th of output amplitude and offset spec per °C for operation outside the range of 18 to 28 °C
[2] Autorange enabled
[3] DC offset set to 0 V
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

The FGA5050 is a function generator that equips with the arbitrary waveform function. In addition to Sine waveform, Square waveform, Ramp waveform of those custom waveform generation function, the FGA5050 offers to realize high precision waveform with 1 µHz of resolution and 50 MHz of wideband frequency. The FGA5050 can be used in wide application such as “Voltage variation test for Automotive Electronic Component”, “ECU false signal source”, “Charge-Discharge test for the rechargeable battery”, Ripple super-impose test” an it can be used as the trigger signal for the various typ of test system.
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Application
Voltage variation test for Automotive Electronic Devices ….
Measurement of the output impedance of the power supply …
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...
(Could not be pasted, must be written manually)

Conclusion: It is possible to find (but rarely) very low frequency generators <1 Hz for testing electronic devices, but not for driving/controlling any test equipment like tensile strength tester. Some devices offers such low frequencies only for ramps.